from the legal standpoint. he struck another individual, regardless, it was an assault. he should be reported at the least, but I do understand what you did and the actions that you took. you handled the situation as best as you could without resorting to any physical confrontations. this is a good thing. bad thing is that you saw the son's face. now this may be an isolated case, but with 20 years experience as a cop behind me, I can honestly say that it in all probability wasn't and isn't....it's a power thing...some people look at others as weaklings and decide to take matters into their own hands and treat others with contempt...
personally, I don't like confrontations that could possibly lead to a physical altercation....but in this case, I think that some might have been warranted. you just don't go hitting on a kid....yours, mine or others....you just don't do it....
I applaud you in what you did and what you are going to do to show that behavior like this is not going to be tolerated....but do so from a position of power...let him know, in no uncertain terms, that you WILL report the next case...and you don't have to witness it...if the youngster shows up even looking like he's been assaulted, you let him know that you will call the cops...don't let him intimidate you like he does with his family...
just sayin... you did good....