Where in the u.S. Is there too much natural fluoride for children?

A few places... Most municipal water supplies are regulated to make sure Fluoride levels are safe. Well water, of course, is not regulated the same. There are testing kits you can buy if you are concerned that will allow you to test the level of Fluoride in your water.
Several places... One of which is in oklahoma: http://www. Ncbi. Nlm. Nih. Gov/pubmed/1985235.