"Really? Cuz you guys all look really young."

I'm the type of person to laugh in awkward situations so I just laughed and said "well thanks I guess we'll all take that as a compliment." These three kids, the boy in particular, then went on to talk about my male supervisor directly "especially him. He literally looks like he's 12. Like is he even old enough to be working here?" Let me just take this moment to say that my male supervisor did just graduate from the college this past May. So he is still young (early 20s) but he does NOT look 12. However he is short and doesn't have a distinctive "masculine" look (no facial hair, not a deep voice etc) but he is the sweetest person. And I could tell that these kids remarks really hurt him. He pretended not to hear as he was sitting at the other desk but his face got beet red and he looked so embarrassed. I was so angry at these kids for saying that but I had to remember my role as customer service first and foremost so I just kind of frowned and said to the kids "that's mean to say." Meanwhile I was blown away that they would be so disrespectful as to say something like that to a faculty member!! I feel like this is a totally different situation than telling a woman she looks young, it's like they were trying to emasculate him. When they left I just turned to him and gave him a sympathetic smile and said "saying you look young is a compliment" just because I didn't want him to feel bad. But now I feel like I should have said more to those kids!! I feel so guilty like I just watched it happen and didn't do anything. I'm now contemplating emailing my supervisor apologizing for those students actions and telling him how bad I feel for their remarks. Should I do that? Or just drop it to avoid embarrassing him further?