Hi, all (again):
DS13 has several friends in our apartment complex. He is among the oldest boys; the youngest ("Bobby" of Bobby and Hannah) is 10. DS came in very upset this afternoon and told me that the bigger boys wanted to play a game called "Flinch" with Bobby. They would pretend to poke him in the eye, and if Bobby flinched, one boy could punch him two times

. DS stuck up for Bobby, telling the other boys that someone could get really hurt and that punching wasn't a game. Then he escorted Bobby to our apartment on their bicycles and told me the story (backed up by Bobby).
When the other 4 or 5 boys involved inevitably showed up, I went out and told them all that if I heard of any more punching games, especially against Bobby, I would have to go to their parents. Although most of the boys aren't very big, three have martial arts training. I know that boys roughhouse, but I'm proud of DS for speaking up at whatever cost to himself (I told him to expect the boys to give him the "business", hopefully just words).
Do I go to the main instigator's parents anyhow, whom I don't know, and if so, how? Should I tell Bobby's mother, who is a friend, and if so, how? Or just stay out at this point?