Children encounter fluoride two ways: topically from toothpaste and mouth rinses, and systemically from the water supply. The fluoride in toothpaste and mouth rinses helps to make the teeth stronger against tooth decay by getting incorporated into the enamel. The fluoride from the water supply gets ingested into the body and deposited into the enamel of the developing permanent teeth that have not yet erupted. Thus, these teeth will already be stronger against cavities when they grow into the mouth. If you do not have fluoride in your water supply or if you use only bottled water, your child may need a supplement. It is important that parents ensure that the child takes his/her fluoride supplements.