It's all fun and games until someone loses an eye.

This American Life did a piece called "The Cruelty Of Children." It's an hour long, and well worth the time. Act One is light-hearted and funny (for a story about taunting, anyway), and Act Two is particularly chilling. Act Three goes into a new idea that should be implemented in every kindergarten class if we want children to grow up to be kinder and less elitist adults.
Take a free hour and give it a listen.