I'm sorry... I appear to be experiencing some technical difficulties with responding to your question. We're trying to fix it. If this actually posts, I'll try to respond again. Thanks for your patience!
Well, finally, it appears that I can reply to your post. (There were a few glitches apparently).
Thanks for your reply to my queries and, again, my apologies that I couldn't respond more quickly.
You have reason to be concerned about your son's behavior... reason enough to see a licensed mental health professional (LMHP). I would contact his pediatrician or your family doctor for a referral to an LMHP who works with adolescents. (I wouldn't recommend a psychiatrist (for medication) or someone who specializes in sexual behavior... start with a generalist-LMHP who can grasp the global picture.)
Why go to an LMHP? Because it is important to diagnose whether or not your son's behavior reflects an underlying mental disorder related to sexuality (such as a paraphilia), related to mood/thought processing, or to impulse control. It is also possible that your son just demonstrated very poor judgment and would benefit from sitting down with someone to figure this all out.
Once an LMHP has a better understand of your son's behavior (and the reasons behind it), s/he will be better able to (a) diagnose the problem and (b) design an appropriate treatment protocol to address the problem.
Your son is very fortunate that, at this time, he was not arrested for his behavior. In some states, if convicted, he could be jailed for committing a felony and (again in some states) placed on a permanent "sexual criminal" list... which would have long-lasting occupational, living, social, and economic repercussions. Use this, then, as an opportunity to get him in to see an LMHP. If nothing else, should this event occur again, it will demonstrate to the legal authorities that you have been trying to address this problem.
I can only imagine the heartache (or anger or confusion or frustration or embarrassment... or all of the above) that this may be causing you. Please remember that this young man is the same 5 year old you helped to ride a bike - and the same young man who may one day be the father of your grandchildren. That is to say, you may be dumbfounded right now with his behavior - but give him time to get some healing under his belt - so he can become the kind of son your whole family had been planning for all along. Please, get him to an LMHP.
Thanks. Best of luck to you and your son.
***FEEDBACK WELCOME. I apologize again for the technical delay.