If you remember being young, kids can be cruel. Usually they
   restrict it to the playgrounds with other kids but, given the
   right (or wrong) stimulus, they can do it anywhere. The only
   thing holding them back is their small stature. Thankfully, most
   kids *do* grow out of this kind of "wild" by 10/12 yrs old, but
   some continue... and those kids who don't learn by then as
   teenagers _are_ problems because they're bigger and stronger.
   But thankfully, most kids grow out of this type of stuff.