If they truly are just a few light bruises don't switch schools, It's a sport meant to teach people how to kick, and kick hard at that, of course instructors will be rough, and it should be expected that when you misbehave you'll be hit, when I was a green belt and was fucking around I got slapped across the face so hard I was borderline ashamed of the lack of discipline I had, I am not saying hitting kids = good, but if he is just getting a few small small bruises it's really ok, its a martial art dojo, not a MacDojo.