You should start brushing your child's teeth as soon as they start to come in and assist with brushing until they are old enough to tie their own shoe laces (around age 7). For children 3 and younger, try and brush for 20-30 seconds without any toothpaste first. After you see the teeth and gums look clean, you have let them take over with a rice size amount of fluoride toothpaste. Try having the child lay down (like on the changing table before a diaper change) when you brush so that you can easily see all the teeth. For children over 3 years of age, brushing should be twice a day for 1-2 minutes. This is also an ideal time to have them start flossing or transitioning to an electric toothbrush. An adult needs to check every evening before bed that the teeth and gums look clean of food or plaque. If they did not do a good job, go back and assist them with brushing, especially along the gumline.