Not all of a child’s teeth are replaced. Children start to have milk teeth erupt at around 6 months of age, and by the age of 5~6 years old there are usually 20 milk teeth, mainly the middle incisors, lateral incisors, first molar, intermolar and second molar, which start to be replaced by the age of 6 years old, and all of them need to be replaced. The first permanent molar will also erupt around the age of 6, which will not be replaced, and the second permanent molar, etc. will also erupt behind the first permanent molar around the age of 12-13, which will also not be replaced. To summarize, not all children’s teeth have to change, so should pay attention to protect the teeth, if the milk teeth have caries and other problems, will also affect the growth of permanent teeth, it is recommended to pay attention to oral hygiene, morning and evening brushing, rinsing after meals, avoid eating too much sweet food. If there are abnormalities in the process of tooth replacement, it is recommended to take the child to the dentist in time.