Flossing It is important to start flossing your child’s teeth as soon as they begin to touch each other. Around two to two and a half years old. Flossing makes a big difference in the prevention of cavities. Generally, when your child starts a kinder garden, they should be able to begin flossing their teeth. Though they may not have the skills yet to do a good job, you should supervise and give tips and pointers now and then to encourage good oral health care. Just like adults, a child should floss their teeth every day. A good time is right before they go to bed, but as long as they floss each day, that is important.