Little boy slapped my son

So we were at McDonald’s in the play area with my 1 year old and 3 year old son. There was a handful of other kids including this other little boy who was maybe 2 or 3 years old. I noticed this little boy chasing a little girl to the point of her crying but assumed they were brother and sister and thought the family behind me was their parents, they weren’t intervening so I just ignored it. 🤷🏻‍♀️

At this point we grabbed a table and my husband comes in with our food. He goes to see what my 3 year old is doing and walks in on my son running inside this little caged area around the 2/3 year old. Literally out of know where the little boy slaps my son, I guess for running around him, ... and hard. My son had a red spot on his cheek. My son started to cry and my husband grabbed the little boy by the hand asking out loud “who’s kid is this?! He just slapped my son and that’s not ok”. Everyone just stared at him blankly...

Since no one was responding he walked the little boy in the main lobby and asked the same thing. A family who didn’t speak English took the boy and just looked at my husband confused.

My husband then came in and told my son “next time someone hits you like that for no reason, you’re allowed to hit them back to defend yourself”. I don’t think my sun understood as he was more interested in getting a hug and running off to play more.

So what do you think? Was the situation handled appropriately? What would you have done?