You did a good thing, Razzle! But it saddens me to hear of such bullying! Was this at a school playground, during school hours? If so, there should have been adult teachers supervising. If that is the case, you should call the school and speak to the principal about what you witnessed, and what you did! The administration should know of things like this going on, and they were lax and even at fault if no adult was out there supervising. I teach, and we must always be watchful and "on duty" during playground activities.
Of course, if this was at a public playground in off hours, then you did the only thing that can be done.
Patty
P.S....OH, I see it was at an elementary school. Is school in session there or on some kind of break. If school is in session, then you should definitely call the school.