Personally, it's usually from a family that beaten them up that causes them to beat their children up also. Kinda like a cycle. It keeps going and going until someone in the family decided not to do that and do a different thing. Same thing with getting pregnant. Don't you notice that the mother gets pregnant soon, the child learns that the mother was pregnant at a young age and does the same thing?
Anyways, my sister gotten beaten up by her boyfriend and is still with him. I was like, "Why are you still with him?! Get out of there before things get worse!" She didn't listen to me. At least her boyfriend cut that habit out of him but I still don't trust him. I refused to talk to him though, and yeah... It should stop and I have friends that got beaten up by their parents too. I would do anything to protect them and I would give them a place to hide from their parents who beats them up, or any relatives.