Our nephew punched my son

So over all I like my in-laws. Some of the kids are well behaved, some of them aren't. This nephew is 5, my son is 4. So pretty close in age, but this boy doesn't listen for shit. I hate to bash someone's parenting because if it works for the child, who cares. But the parents have no control because they don't stick to any repercussions, they care about his feelings more than punishments. Normally, it's whatever, but your child hurt mine!Well, I wasn't there when this happened, but my husband was. So nephew grabbed my son by the shirt and straight-up punched him in the face with intent. He made my son's nose bleed. Nephew's father was in the other room, so my husband stepped in. He put nephew in time out and yelled (loudly and sternly) at him. Then talked to nephew on why He did it... 'because (son) roared at him'. Then DH explained that is the wrong reaction ect. He handled the situation better than I would.Anyway, I don't want to make a thing of it because DH already handled it and told both parents about the incident. But I am PISSED. This child has no repercussions for his actions. If my son did that I'd woop him silly and leave the house. Not for this child, when nephew's father walk in (hearing DH yelling at his child, somewhat on defense) nephew got a 'oh you shouldn't do that'. STFU and take a toy away or something, ANYTHING!I'm looking for ideas of a passive way for the next family event to approach this if it happens again.Edit- On top of this kid hitting mine, my son has a brain condition (Chiari). So any hit to the head (or any minor incident) could potentially mean surgery. I'm a little over protective of that beautiful head of his. via /r/Parenting http://bit.ly/2LJaCkj