The idea that all teeth are replaced in children is not rigorous. Legally, a child is anyone up to the age of 18, and at 18 basically all adult teeth have been replaced as well, so these adult permanent teeth are definitely not replaced. Even if we take the age of 0-14, which is often referred to in medical terms as a child, the period of tooth replacement for children is generally past. The permanent teeth that are replaced at this time will not be replaced either. To be precise, all the baby teeth of children will be replaced. If we have to put a limit on the age, we generally think that all the teeth erupted before the age of 3 will be replaced. There are 2 sets of teeth in a person’s life, 1 set of milk teeth and 1 set of permanent teeth, and the milk teeth will be erupted by the age of 3. There are 20 milk teeth, which will be replaced gradually during the period of tooth replacement. The so-called tooth replacement period, generally refers to 6 years old to about 12 or 13 years old, but due to the increasingly good nutrition of people nowadays, many children change their teeth earlier, some children even at the age of 5 years old or even less than 5 years old began to replace teeth, so it is not strict to simply say that only after the age of 6 years old began to replace teeth.