This story says 1 in 200 kids are vegetarians these days, and they quote a UNC Asheville scientist to back it up:
The new estimate of young vegetarians comes from a recent federal Centers for Disease Control and Prevention study of alternative medicine based on a survey of thousands of Americans in 2007. Information on children’s diet habits was gleaned from about 9,000 parents and other adults speaking on the behalf of those under 18.
”I don’t think we’ve done a good job of counting the number of vegetarian youth, but I think this is reasonable,” Amy Lanou, a nutrition scientist at the University of North Carolina-Asheville, said of the government estimate. She works with the Physicians Committee for Responsible Medicine, a vegan advocacy group.