Children’s head size may be related to physiological reasons such as congenital heredity, and may also be related to pathological reasons such as hydrocephalus, intracranial tumors and other diseases. 1. Physiological reasons: If both parents have a large head, the child’s head circumference may be larger than other children’s during growth and development due to the influence of genetic factors. If it does not affect the normal physical and intellectual development, there is no need to worry too much. 2. Hydrocephalus: Usually the fontanel will not close until the child is one to one and a half years old. If the fontanel closes too late, the intracranial pressure may increase, and then hydrocephalus may occur. 3. Intracranial tumor: If there is a tumor in the skull, it may affect the closure of fontanel, and the closure time may be later than that of ordinary children. At this time, the head circumference may also be large, and may be accompanied by irritability, nausea and other symptoms. 4. Vitamin D deficiency rickets: some children may develop vitamin D deficiency rickets due to the lack of timely supplementation of calcium and vitamin D during growth and development. It shows the phenomenon of large head circumference, and may also be accompanied by other calcium deficiency manifestations such as chicken breast. It is recommended to go to the hospital for timely examination such as cranial imaging, blood calcium level examination, etc., in order to exclude pathological causes. In daily life, it is necessary to supplement calcium and vitamin D in time to avoid adverse consequences.