Infants can be made to laugh after 2 months of age, can laugh out loud after 3 months of age, and can smile voluntarily when they meet people. Smiling is an early sign of the development of language function. After a few days of life, spontaneous smiling may occur in newborns. After 2 months, infants can be teased, after 3 months they can laugh out loud, and they can initiate smiling when meeting people. Communication between family members and infants, such as talking and singing, can stimulate the child’s desire for expression, and the infant’s contact with more people is beneficial to the development of the child’s language function and intelligence. If a 3-month-old child still cannot be made to smile, has few facial expressions and is unresponsive, this is a sign of developmental delay and should be promptly evaluated by a pediatrician for growth and development. In addition to monitoring changes in height and weight after birth, it is also necessary to pay attention to the development of the pediatric neurological system and to promptly visit the pediatrician for treatment of any problems.