This week's issue of Sports Illustrated has an excellent article about kids and overuse injuries in sports. It focuses on the injuries received when kids choose, or are encouraged to choose, one sport to play--many of them year round. It states that kids who play one sport exclusive to other sports are developing high rates of injuries than kids who play several sports.
For example, kids who decide to play exclusively tennis at an early age develop more injuries than kids who play a variety of sports throughout the year.
http://vault.sportsillustrated.cnn.c...4189/index.htm