Infants, toddlers, young children, and children are usually classified according to age. 1. Infants. In clinical practice, infants are defined as the period from birth to one year of age, which is the first peak period of growth and development, but are prone to digestive disorders and nutritional disorders. 2. Toddler. This is the period from one year of age to three years of age. As the brain development of children gradually improves, they are more curious about the outside world, which makes them prone to accidents and injuries. 3. Pediatrics and children. Pediatrics and children belong to the same concept, usually including infants, toddlers, preschool, school age and so on. The preschool period is mainly from three to seven years old, which is the key period of intellectual development, and the speed of development is faster. The school-age period is the period from the age of seven to pre-puberty, when all organs except the reproductive system have developed close to adulthood. If your child develops symptoms that are different from those of other children of the same age, it is advisable to consult a pediatrician. It is recommended to consult a pediatrician in a timely manner to clarify the cause of the disease under the guidance of the doctor and then treat it.