We often meet parents who ask “What is the best age for children to have their teeth straightened?” We often answer this question with “We work differently at different ages, even when the teeth are in their early years”. Here I will describe each of the different ages. First of all, the period of milk teeth is the period from the eruption of the first milk teeth to the eruption of the first permanent teeth, usually from half to six years old. During this period, the most common malocclusion in children is the anterior teeth “enamel”, i.e. the lower front teeth are wrapped outside the upper front teeth, while the upper teeth should be outside and the lower teeth inside. The best time to treat this malocclusion during the milk teeth period is 3 to 4 years old, which can be extended to 5 years old for children with late tooth replacement. It is necessary to correct the malocclusion during the milking period because, firstly, the correct direction of growth of the milk teeth will lead the permanent teeth to erupt in the correct direction, and secondly, there is a rapid growth period when the child is 5-6 years old. Second, there is a rapid growth period when the child is 5-6 years old. Secondly, the period of tooth replacement is the period from the eruption of the first permanent tooth to the completion of all the milk teeth, generally from 6 to 12 years old, during which the most frequent malocclusion is still the anterior teeth, but the situation is more complicated. “In this period of time, children are more likely to have another malocclusion, i.e., maxillary protrusion or mandibular recession, or both, which is manifested by the appearance of the upper front teeth are more prominent, for these two malocclusions doctors need to analyze the X-ray film to determine the pathogenesis, and then develop a different orthodontic program. This is the period when the child’s skeletal development is so rapid and plastic that proper intervention can yield twice the result with half the effort; on the contrary, if this period is missed, some malformations will develop to the point where they cannot be corrected by orthodontic methods alone. However, there is no need to rush to correct the simple malocclusion in this period. Thirdly, the permanent period, when all the baby teeth in the mouth are replaced by permanent teeth, is generally after 12 years old. At this time, we have to correct the malocclusion, dental maxillary protrusion, dental mandibular protrusion and dental bimaxillary protrusion. For those bony deformities, we have to wait until after 18 years of age for combined orthodontic and orthognathic treatment. Children have a high growth potential at the age of 12 to 13 and teeth move faster, so the course of treatment will be relatively short. However, our alveolar bone is malleable for life, so the age of orthodontic treatment is not a problem, but the best period must be grasped.