At 4 1/2 months, babies can usually roll over and sit up when supported on their hands or hips. At 3 months, babies can usually lift their chest with hand support in the prone position, so usually by 4 1/2 months babies are also already rolling over. At 5 months, babies can hold toys in both hands, and can consciously cry and laugh. At 8 months, babies can sit for a long time, change toys from one hand to another, and can pronounce complex sounds, such as “mommy”, and can understand their own names. Parents should pay more attention to accompany the baby, pay attention to infant education, balanced nutrition, if the baby’s motor development has a significant lag, should consult a doctor in order to clarify the cause of the disease, standardized treatment.