Is it his son,or his girlfreinds and some other guys son?
My Dad Works with cases like this and he was telling me alot of times,when girls have kids from other guys and the hook up with a new guy,the guy dont really care too much for the kid,especially if he dont like the father of the boy,so when they discipline the kid,it has a little hate behind it...or something like that.
We all had beatings from our parents,I hit my kids,but I dont BEAT DOWN on them.What that guy did was too far.Stomping a kid......WTF?! Someone should stomp him.