Wait until the social workers get them and tell them why they are victims. Why this was wrong, bad, dirty. And get them to accept they were victimized and adopt a victim mentality. we've seen that before.
If it was my son, i would not allow them near him if my son actually wanted sex and desired the woman. I would have a talk with him. I would make sure he understood why this person will be punished. That they abused their position/age while saying that while he might feel lucky (and I would have too at his age) and this is something many young men fantasize about that he got to live, he still needs to understand why what she did was wrong, even it felt so right to him.
I might give him a subtle high five with a smile saying 'but we are not celebrating this' as I walked away.
i would not allow anyone to convince my son he was a victim.