Children need no encouragement to be violent. It comes quite naturally. In fact without learning about the effects of violence through play, a person is much more likely to be dangerously violent when they grow up.
I think kids see slapstick as a game because manifestly no one gets seriously hurt while there is a lot of action. I doubt the fire house gag has ever made anyone want to beat someone up, like say,
300 doees. If they try and replicate it (or a three stooges gag) they will quickly find out how hard it is to time right and give up pretty quickly. (or at least me and my brother did
)
Play, Spirit, and Character [Speaking of Faith® from American Public Media]