well, i know you arent really talking about broken bones anymore, but i remember when i was like in 3rd grade, my friend decided to do a backflip off of the top of the monkeybars. needless to say he broke his arm so bad he had to have 2 or 3 surgeries and several screws in his elbow.
another time, was when my mom was in 5th or 6th grade. she was riding her bike without her glasses and got hit by a car! well, she didnt tell her parents and after a day or two she finally told her dad what had happened. her arm turned out to be broken in 5 places.