The normal performance of three-month-old babies usually reflects in physical appearance, movement, vocalization and communication. 1. Physical appearance: three-month-old male infants weigh 6.3-7.9kg and their height is 61.3-65.5cm; female infants weigh 5.8-7.2kg and their height is 59.7-64.1cm; however, due to different nutritional conditions and genetics, there will be variations among different infants. 2. Movement: Motor function begins to develop gradually in this period, at this time, not only can they lift their head up, but also can support the upper part of their limbs with both elbows, while the spine of the neck begins to develop and bend forward. At the same time, the spine of the neck begins to develop and bend forward. In addition, infants have begun to try to roll over at this time. 3. Vocalization: When a normal infant reaches three months of age, the speech center will be developed to a certain extent, and generally can produce babbling sounds, and the language function will begin to be perfected initially. 4. Communication: Normal infants begin to try to communicate with the outside world at three months, and some infants can laugh out loud. Some infants can laugh out loud. Especially when parents interact with and tease their infants, the infants can respond accordingly, such as being amused. If the above aspects of the performance of three-month-old infants are not normal, it is recommended to consult a doctor in a timely manner, with the help of the doctor to identify the cause of the disease, and targeted treatment or therapy.