A: I'm glad to hear that you're brushing your son's teeth twice a day. You should be using non-fluoride toothpaste at this stage to avoid having him swallow too much fluoride on a daily basis, which can cause staining on his permanent teeth. The plaque that builds upon teeth is not from food, by the way, but bacteria. It would probably help if you brush his teeth along the gums, as this is where the plaque usually starts forming. Also, visit a dentist now to be sure there is nothing wrong.