It takes many years before children develop the fine motor coordination they need to do a good tooth brushing job. Some dentists advise that parents brush their children's teeth until the child can neatly write his or her own name. Other dentists suggest parents use their own judgment, but to consider between ages 6 and 8 as the time for kids to take on the job of keeping their teeth clean and healthy. General rule: A smear or pea sized drop of fluoridated toothpaste can be used when the child can spit effectively.