Sleep disorders are rarely diagnosed in infancy and early childhood. By analyzing a range of risk factors for sleep disorders in infancy and early childhood and empirical data affecting sleep, this paper proposes the following: namely, that the influence of both parents’ behaviors on the autonomy of the child’s sleep is a fundamental problem that leads to sleep disorders, such as both parents staying with the child until the child falls asleep and then putting him or her to bed. Chronic sleep deprivation in childhood has serious potential implications, with at least three components of development directly affected: behavioral and social competence, cognitive ability, and physical health status. Even after controlling for potentially complex variables, children with intermittent nighttime short-sleeping behavior before age 3.5 years had a higher risk of hyperactivity-impulsivity and low levels of cognitive functioning at age 6 years than did children who slept for up to 11 consecutive hours per night. In addition, children who had continuous intermittent short sleep in early infancy were at greater risk of being overweight at age 6. For optimal growth and development, the National Sleep Foundation Poll recommends 10 hours of sleep per night in early childhood. (I) Normal sleep development 1. Sleep duration and firmness The total sleep duration of a full-term baby is about 16-18 hours per day after birth, and decreases gradually with the growth of the baby. 13-14 hours per day at the age of 6 months, and 10-11 hours per day at the age of 6 years, with an average of 2-3 naps per day during the daytime before the age of 6 months (a total of 3.5 hours), and 2 naps during the daytime between the age of 9-12 months, and 2 naps after 18 months to the age of 3 years, and 2 naps during the daytime after 18 months to the age of 3 years. and one afternoon nap per day (2.5 hours) after 18 months through age 3. About 68% of children gradually stop napping at 4 years of age.1 At 6 months of age, the duration of continuous nighttime sleep is up to 6 hours, and at 1 year of age it reaches 8-9 hours. An Italian study showed that the longest duration of nighttime sleep for infants aged 6-12 months was 8-9 hours, and for toddlers aged 13 months to 4 years, stable sleep patterns lasted up to 9 hours per night. In preschool, the duration of sleep at night basically stays at about 10-11 hours per night. The development of sleep and wakefulness Sleep and wakefulness are regulated by two processes, namely, circadian rhythms and homeostasis.2 (1) Circadian rhythms (Pocess C), also known as “biological clocks”, are mainly controlled by neurons in the supraoptic nucleus of the hypothalamus. Immunocytochemical observations show that the supraoptic nucleus develops early in human gestation, i.e., at the 18th week of gestation, and gradually takes shape in the first trimester of gestation, and then matures after birth until the age of 1 year, when the number of posterior lobe pressor neurons reaches the adult level of development. Rhythmic changes in the biological clock are controlled by a combination of transcriptional activators and cytochromes. Since the intrinsic rhythm of the suprachiasmatic nucleus is not precisely 24-hour, it needs to be regulated daily to prevent deviation from the alternating day-night cycle. Light signals are transmitted through a key neurotransmitter pathway, the retinohypothalamic tract, which causes the rhythm in the suprachiasmatic nucleus. This pathway is present in humans at birth.3.4 In newborns, sleep-wake rhythms are free rhythms that are not influenced by the 24-hour cycle or external conditions. At one month of age, the length of the daytime and nighttime sleep rhythms is only 3-4 hours. At 6 weeks after birth, the time of daytime wakefulness increases, and by 12 weeks after birth, the nighttime sleep time is longer than the daytime sleep time, and the time of wakefulness and sleep stabilization gradually take shape to form a circadian rhythm. External synchronizing factors (e.g., light-dark cycle, noise, social interactions) make it easier to establish a biological clock. Different biological clocks (e.g., body core temperature, melatonin) develop at different rates. For example, body core temperature begins to change with the biological clock at 1 week postnatal, while melatonin secretion occurs until approximately 1.5 months and cortisol secretion occurs 3-6 months postnatal. (2) Internal homeostasis (Process S) i.e. Process S is different from circadian rhythms and is not easily defined by neurophysiology. Homeostasis is marked by different signals: e.g. NREM phase 4 and low frequency range EEG (0.75-4.5 Hz, Delta wave or slow wave activity). In humans, the C-process is active at birth, whereas the S-process is active until 2 months after birth. The gradual decrease in crying during the first two months of life can be explained by the influence of the S-process, which reduces the intensity of the “wake-up signal” (controlled by the C-process) at the end of the day. Infants often need to take naps, and the need decreases with age. As infants become able to sustain longer periods of wakefulness, the rate of accumulation of sleep stress (controlled by the S process) decreases with age, leading to a paracrine degradation of the need for naps.5 During the day, the “awakening signal” of the C process is enhanced, counteracting the accumulation of sleep stress. Similarly, at night, process C and reduced sleep pressure neutralize each other, thereby inducing arousal the next day. In short, the interaction between the C-process and the S-process develops, resulting in prolonged wakefulness during the day and stabilization of sleep at night. (II) Sleep abnormality 1. Definition and epidemiology Sleep abnormality is defined by the American Diagnostic Standard for Mental Disorders DSM-IV as a group of disorders characterized by difficulties in sleep onset or maintenance. In infants and young children, sleep disorders are mostly difficult to diagnose. Recent studies have categorized sleep problems in infants and young children into two groups: (1) frequent nocturnal awakenings: >2 awakenings per night in children aged 1-2 years, and >1 awakening per night in children aged 2 years and older. Difficulty in sleep initiation: children 1-2 years old fall asleep for >30 minutes, children over 2 years old fall asleep for >20 minutes. Sleep disorders are categorized into 3 degrees: ①Normal (≤1 time in 1 week) ②Mild (2-4 nights per week) ③Disordered (5-7 nights per week for more than 1 month) According to family data and sleep laboratory statistics, from birth to 3 years of age, infants and children wake up an average of 3 times per night, except for the child’s own reaction (e.g., some children do not show obvious awakening signals or the child is able to self-soothe himself/herself to sleep). At birth, 95% of infants have a significant nightly awakening, at 5 months of age, 20% have at least 1 significant nightly awakening, and by 1 year of age, most young children are able to independently fall back to sleep through self-soothing. Sleep onset latency averages 15 ± 10 minutes throughout infancy. Difficulty falling asleep is defined as falling asleep for longer than 30 minutes. Frequent nocturnal awakenings tend to occur in infants and toddlers younger than 2 years of age; difficulty falling asleep tends to occur in older children, especially at 4 years of age: 6% at 1 year of age, 12% at 2 years of age, 24% at 3 years of age, 49% at 4 years of age, and 33% at 5 years of age. About 10% of infants and young children have two sleep problems at the same time. 2. The etiology of sleep disorders in infancy and early childhood Both nocturnal awakenings and difficulty falling asleep are associated with disruptions in sleep stability, which leads to the phenomenon of short sleep that persists over time. Sleep disorders, or sleep fragmentation, are influenced by a combination of biological (maturation of the central nervous system, personality and temperament of the child, genetic inheritance) and environmental factors. (1) Infants’ own traits It is currently believed that infants’ own traits have an impact on the establishment of sleep firmness. ① It has been found that children aged 8-11 years who were born preterm have a relatively high sleep apnea index (apnea index) apea-hypopnea index and lower oxygen saturation compared to children of the same age who were born at term. (ii) Gender: by and large, there is no major effect on the establishment of sleep firmness. (iii) Difficult temperament: associated with sleep problems. Preschoolers with difficult-to-nurture temperaments exhibit: irritability, anger, susceptibility to environmental influences, crying, and more reactive behavior, as well as being more likely to experience significant nocturnal awakenings. A representative population-based survey showed that for poorer sleep firmness, difficult-to-nurture temperament was a significant independent risk factor. On the other hand, children with sleep problems have a higher rate of having a refractory temperament and higher scores on the Emotional and Behavioral Problems Scale (EBPS) than children with better sleep. It is difficult to identify the cause and effect of this problem. Organ dysfunction: Children with gastrointestinal reflux, hiatal hernias, and milk allergies are more likely to have sleep problems. Infants and young children with gastrointestinal reflux are more likely than normal to have difficulty falling asleep and waking up at night. ⑤ Neurodevelopmental disorders: such as autism, attention deficit hyperactivity disorder, hyperactivity and obscenity syndrome, and mental retardation due to hereditary syndromes are all prone to sleep disorders, which can be characterized by difficulty in falling asleep, frequent nighttime awakenings, and early morning awakenings. These can be controlled and treated by environment and medication. (2) Parental causes Parental behaviors may also hinder or promote the development of sleep firmness. Anxiety, overprotection, and depression can all contribute to a high incidence of sleep disorders. Mood depression has been studied more extensively, and it is thought that the more likely mechanism by which it affects sleep is that mood disorders in depressed mothers lead to overprotection, which affects the infant’s autonomy in sleep.6 On the other hand, the mother’s age and level of education also have an impact on the infant. ① Behavior of both parents during sleep: A longitudinal study has shown that specific behaviors of both parents, such as both parents accompanying the child to sleep, and the child waking up at night and going to sleep in the same bed with both parents, are the earliest early warning signs of sleep problems in infancy and early childhood.7 Parents who stay with the child until he or she goes to sleep, or who put him or her down after the child goes to sleep, prevent the child from learning to go to sleep on his or her own, and thus, when the child wakes up at night, it is much more difficult for the child to go back to sleep on his or her own. When the child wakes up in the night, it is much more difficult for him or her to fall back to sleep on his or her own. In order to train a child to fall asleep on his or her own, it is necessary to correct certain behaviors of both parents before the child goes to bed. Behavioral interventions must include the parents in order for treatment to be effective for most sleep disorders in infancy and early childhood. Effective identification of the child’s sleep problems can improve the quality of life for the family. ② Biparental Behaviors After Nighttime Awakenings: A large sample size study found that some behaviors of both parents toward their child’s nighttime awakenings were associated with the emergence of sleep fragmentation.7 For example, feeding after nighttime awakenings in infants after 5 months of age resulted in fewer than 6 hours of continuous nighttime sleep per night. One study showed that unweaned children had shorter nighttime sleep durations than weaned children. At this stage of infancy, nighttime feeding after awakening is no longer a physiological necessity, but rather a hindrance to sleep stabilization. In addition, holding the child out of bed for comfort (rather than in bed) after nighttime awakenings was significantly associated with sleep fragmentation in infants and toddlers. Carrying the child out of bed interferes with the child’s sleep autonomy (e.g., the ability to wake up during the night and go back to sleep alone by self-soothing). (iii) Breastfeeding (still controversial) Breastfeeding is more likely to result in less than 6 hours of continuous nighttime sleep per night in infants after 5 months of age compared to artificial feeding. On the one hand, the faster digestion of human milk than formula shortens the time to satiety, and on the other hand, one study observed that infants still slept better when mothers delayed breastfeeding slightly after the onset of hunger manifestations (the same delay was used for artificial feeding to prepare bottles, etc.). There is no doubt about the value of breastfeeding, not only is it beneficial to both mother and child, but it also creates a bond between mother and child. ④ Co-sleeping In the West, it is considered that starting to sleep alone is a milestone for starting to get a good night’s sleep. In fact, co-sleeping or sharing the same room with another family member can cause infants and toddlers to sleep less than 6 hours of continuous sleep per night. Sleeping in the same bed with a parent to soothe a child’s nighttime awakenings can lead to additional sleep problems, especially for children over the age of 4. The majority of children with sleep disorders sleep in the same bed as their parents (70%). Of course there are many other causes whose combined effects cannot be distinguished. ⑤ Problems in the family, environment, and habits In the case of many external factors acting together, there is not much correlation between these problems and the emergence of sleep disorders. 3. Effects of long lasting short sleep Sleep problems have adverse effects on the growth and development of children. (1) Behavioral functioning There is much evidence that daytime behavioral problems are associated with sleep problems.8 Among children and adolescents with chronic persistent short sleep, many drowsy behaviors occur during the day, ranging from typical drowsy symptoms (e.g., yawning) to overactive hyperactivity and impulsive behavior. Subjective studies have shown that sleep disorders are associated with ADHD, with children having mostly poor nighttime sleep and more nocturnal movements, yet laboratory tests suggest that children have normal sleep architecture. Longitudinal studies have found that 6-year-old children who had a history of sustained short sleep before 3.5 years of age were more likely to have higher hyperactivity-impulsivity scores (2.5 times higher) compared with children who had 11 consecutive hours of sleep per night.8 One possible explanation for why sustained short sleep in the early years can lead to this problem later is that early sleep deprivation affects the development of the neural systems that control daytime alertness, particularly the secretion of Hypocretin (a neuropeptide of the sleep-wake system) located in the lateral hypothalamus. In 1998, a researcher9 identified a small molecular peptide synthesized and secreted by the lateral hypothalamic region of the rat, hypocretin.Subsequent neuroanatomy and molecular biology demonstrated that the hypocretin system is involved in the regulation of sleep and wakefulness10 and that it plays a decisive role in the regulation of the wakefulness system, with the activity of the neuron leading to a decrease in drowsiness and an increase in arousal and It plays a decisive role in the regulation of the arousal system. (2) Cognitive function The relationship between sleep and the ability to learn and utilize knowledge has been well documented. Some children have difficulty recalling what they have learned, and these children often have irregular bedtimes and consistently short sleep periods compared to children without memory difficulties. A sleep trial found that increasing sleep duration by 1 hour per night for 3 consecutive nights resulted in better cognitive performance in children with a mean age of 10.6 years. Longitudinal studies have investigated that 5-year-olds who had consistently short sleep in infancy had a higher risk of receiving low scores on the Peabody Picture Vocabulary Experiment (3.2-fold) and a higher risk of receiving low scores on the block design of the WISC-III at 6 years of age (2.1-fold), compared with those who were able to sleep for 11 consecutive hours per night in infancy and early childhood.8 These results suggest that consistently short sleep reduces the likelihood that a child will achieve better academic performance as well as the ability to make good school adjustments. (3) Physical growth In longitudinal investigations, persistent short sleep in infancy and early childhood led to a threefold increase in the risk of children being overweight or obese at age 6 years compared with children who slept continuously for 11 hours per night. The underlying biological mechanisms for this association remain unclear, and several explanations exist. Decreased sleep duration affects the secretion of two key hormones that control appetite. Sleep deprivation causes an increase in Ghrelin secretion as well as a decrease in leptin (leptin) secretion. The high ratio of the two hormones stimulates appetite and may lead to weight gain. Another possible explanation is that prolonged sleep stimulates the hypothalamic-pituitary-adrenergic axis causing an increase in growth hormone secretion and thus reducing the risk of overweight. These two mechanisms are interrelated in that low levels of Ghrelin stimulate slow-wave sleep, which increases growth hormone secretion; on the other hand, high levels of Ghrelin lead to a feeling of hunger, which interferes with sleep and reduces growth hormone secretion, leading to weight gain11. So far, it has been experimentally demonstrated that Ghrelin promotes the release of growth hormone in rodents and humans, and that Ghrelin increases the release of growth hormone in the circulating bloodstream. Ghrelin has been shown to increase circulating GH rapidly, dramatically, and persistently, even more so than GHRH.12 Ghrelin is involved in regulating GH secretion in conjunction with GHRH (Growth Hormone-Releasing Hormone) and Growth Suppressor Hormone (SS), which form a localized negative feedback loop in the hypothalamus. Intravenous, ventricular and intraperitoneal administration of Ghrelin in rats can increase the blood level of GH. Ghrelin can promote the release of GH from cultured pituitary cells in vitro, and studies in free-ranging rats have found that different doses of Ghrelin can cause a dose-dependent increase in the release of GH. (iii) An integrated model of risk factors for sleep disorders and their effects (see figure) A theoretical model of a multifactorial integrated system for infant sleep management was developed in 199313 and modified with empirical data, with the final results shown in the figure. This model, by incorporating a number of different factor regression analyses, first demonstrated the factors that are highly associated with low quality sleep and concluded that, among the many causes of sleep fragmentation and persistent short-sleeping problems, for normal children without neurodevelopmental and organ disorders, the particular behavior of the parents while the child is sleeping (as shown in the figure) is the main contributing factor to the child’s sleep disorder. This is the reason why behavioral therapy that incorporates sleep-related parental behavior training has a 90% success rate. Sleep is also influenced by both the personality traits of the parents (overprotective, depressed, etc.) and the traits of the child (especially difficult temperament), as well as culture, socio-economic status and family structure. But for example, things like the child’s gender, whether or not the child was born prematurely, the mother’s age, level of education, the adoption of transitional soothing objects, income status, etc. do not seem to be significantly correlated with the establishment of sleep stability. This paper emphasizes the importance of children getting continuous sleep every night, and that the minimum duration of continuous sleep should be precisely determined from infancy, although there are individual differences in the duration of sleep required (e.g., short sleepers or long sleepers). In order to avoid sleep disorders in infancy and early childhood, it is advisable for parents to train their children to sleep on their own and to let them go to bed and fall asleep without parental intervention when they are drowsy but still awake.