My son and his friend at school often playfully slap, kick, hit, or write on each other with markers. He came home the other day with marker all over himself and his clothes and said that his friend would not stop writing on him when asked to. Today the same boy hit him in the face three times and thought it was funny. It didn't hurt him, but I think this is getting out of hand. I have told my son that this behavior is not acceptable, as I know that he is not innocent either. They are friends and it is not malicious, but I'm afraid someone will get hurt. Should I get involved or back off?