Ha! Consider the feelings of the OP?? Sadly this is aibu where competitive nastiness is rife. People think the anonymity it brings gives them carte blanche to say whatever the fuck they like, and in fact if they can get a witty insult in, the harsher the better.
When it boils down to it, if my child had their underwear yanked down by another, would I be angry and upset for my child, hell yes! Would I be angry with the child who did it? A bit, yes. Would I want to ensure that the child was made to understand that their actions were wrong, inappropriate and not to be repeated? Also yes.
Would I want them given a good thrashing, humiliated themselves by their teacher, made afraid to go to school, suspended or expelled? Fuck no! They are FIVE!!!
Again, if it was my child who did the underwear yanking, would I feel angry at them for doing something stupid? Yes. Would I feel sorry for the child whose underwear was yanked? Absolutely. Would I want my child admonished, made to apologise and given an immediate and age appropriate punishment? Of course.
But as above, would I want my child thrashed etc? Would I fuck, and not one of the sanctimonious idiots on this thread advocating this for this five year old would want it for theirs either if they had carried out the same action.