A: That's correct. This is a crucial stage in tooth development. The permanent teeth are forming inside the jaws; if they're exposed to a large amount of swallowed fluoride, they can develop with unsightly stains. This is a common occurrence among young children who don't spit out toothpaste during and after brushing. With children younger than 2, it's recommended that you use plain water or a tooth and gum cleaner that doesn't contain fluoride. When your child's older, limit the amount of toothpaste you use to less than the size of a pea until he understands that he shouldn't swallow it.