Our rule of thumb on brushing is that until kids can tie their own shoes, mom or dad need to help brush teeth because they do not have the dexterity developed yet to properly clean all surfaces of their teeth. Up to this age (around age 6), a manual toothbrush is usually sufficient.
Many parents come in telling us that bad teeth “run in the family” and that is the reason their child already has decay. The other issue is that parents tell us that it’s really hard to brush their child’s teeth or that they won’t do it on their own. The good news is that we believe that diet is the biggest factor and something you actually have control of.