Considering the child’s development, there may be the following reasons: (1), separation anxiety: children with separation anxiety often have unexplained midnight crying and are very clingy during the day. For this kind of child, the mother needs to pat him, hug him or whisper to soothe him. (2) Emotions: If the parents (especially the mother) are emotionally unstable, such as anger, frustration, insomnia, tension and anxiety, it is often easy to “infect” the child; if there is a change in family relations, conflict between people or moving, etc., it will put the child in a state of emotional tension and thus crying. (3), activity: children’s nervous system is not fully developed, weak inhibition function. Therefore, too strong stimulation during the day or too intense activities at night before bedtime can easily make the child’s brain still in a state of excitement during sleep, which can trigger sudden crying, like a nightmare. Therefore, it is not advisable to let the child too much activity before bedtime, so that the brain excitability is too high.