So we were walking home and my friends son who has suspected ADHD started hitting my son he is younger than my son by a year and a bit, My son isn't very boisturous so he wouldn't retaliate, my friend was there and I was waiting for her to tell him off to remove her son but she didnt he continued to jab my son in the privates as we were walking along and then slapped him across the face REALLY hard, my friend finally said stop but that was about it she walked off and her son came back up and tried to hit my son again to which I had, had enough and said firmly Stop! He then walked off and started hitting some other children again, my friend pretty much ignored his behaviour and I was left feeling pretty pissed off, I don't see it as my place to tell off someone else's kid when they are there and so expected her to do it, he said to my son he's going to get him back tomorrow, If on the way home he does it again and I intervene if she doesn't am I wrong? I don't know what to do? What would you do?