that does sound alarming - does this boy have older siblings who could be exposing him to pr0n? Even accessing anything his parents may have? Kids naturally like to explore their bodies, but his has gone beyond that and has crossed the line. Kids who are exposed to pr0n/sex etc can act out what they see not realising that what they are doing isn't cool. But I completely understand you not wanting to make a big deal out of it because that could make him feel ashamed of himself and he will keep it a secret from you, especially if it feels good to him. Make him feel good for telling you and say how awesome he is that he can talk to you about it. And while you should definitely talk to his parents, also be aware that they may not be receptive to what you're saying - not many parents would like to hear that their child is doing what he's doing and may even insinuate that it's your boy that's the leader. Good luck.