Tooth decay among children in the US has declined dramatically in the last
20 years. About half of all kids reach the age of 18 without a cavity. Much of
this can be credited to fluoride. Fluoride helps children's teeth by making
tooth enamel harder and more resistant to decay. It helps stop the growth of
newly-formed cavities. 
Although fluoride is found in some foods, most toothpastes, a few rinses, and prenatal and children's vitamins, tap water is the most common source. Studies show that adding fluoride to drinking water prevents 30 to 40% of
cavities. Nearly 2/3 of the water in the US is now fluoridated. So make sure your children drink plenty of water: 
age 6mo.-3 years ......1 Cup
age 3-6 ......2 Cups
age 6-16 ......4 Cups 
If your children are drinking bottled water, they may not be getting the
fluoride they need. Many brands of bottled water do not contain the
recommended level of fluoride. To be sure your child is getting enough fluoride, call your local utility and ask
about fluoride in your water system. If you filter your tap water, make sure
the filter doesn't remove fluoride. If you don't have fluoridated water, ask
your dental hygienist about fluoride supplements.
