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.