According to the seventh edition or the eighth edition of the People’s Health Publishing House of Pediatrics, the first chapter of the explanation, generally divided into seven periods. The fetal period is before birth, the neonatal period is 28 days, within 1 year old is called infancy, 1-3 years old is the early childhood period, 3-6 years old or 7 years old before school is called preschool, 6-12 years old is the school age, after 12 years old girls to 18 years old, boys to 21 years old is called adolescence. 21 years old boys and girls before 18 years old theoretically belong to the pediatric content, because height and weight look like adults, but emotions, control of emotions, etc. are not yet adults. But emotions, control of emotions, etc. are not yet adults, and belong to children who need protection.