Children generally need to replace 20 teeth. In most children, milk teeth begin to erupt 6 to 8 months after birth, and all 20 milk teeth erupt by the age of 2.5 years. When children are around 6 to 7 years old, the milk teeth are gradually replaced by permanent teeth, so children generally need to have 20 teeth replaced. Permanent teeth that come in around the age of 6 to 7 will not be replaced for the rest of a child’s life, so parents should try to get their children into the habit of brushing their teeth in the morning and evening and having regular dental checkups, and should not eat too many sweets and candies in their spare time. If children have dental problems, they should go to the hospital in time for checkups and be treated accordingly.