My heart goes out to you, you must be feeling terrible, and your son may well feel even worse!
When I was a girl, I did this, with my siblings. I don't know why, except that I was curious about my body and about sexy feelings, and I couldn't talk to my mum, she was so prudish and even though she made an attempt to talk to us about sex, it was painfully obvious that it sickened her to do so. The first thing she ever told me about sex was that it was something dirty old men did to little girls! My siblings and I dont discuss what happened, and we are all pretty embarrassed and troubled that it happened.
My husband told me that he and his brother similiarly experimented when they were kids, and their family was as permissive as mine was restrictive. So, the true reasons for such experimentation remain a mystery to me. Maybe lots of kids do it, as you said, and dont remember or dont tell anyone.
You probably feel responsible for how your friend is feeling now, and how this might affect her son, but your main concern needs to be your own son. He probably wants the earth to swallow him up. So, as I'm sure you already have, let her know how sorry your son feels, but concentrate on your son.
You need to get around his embarrassment so that you can address this, because its really important that he doesnt repeat this behaviour. You mustn't tell him off, or worse, punish him. Tread really carefully, but at the same time, let him know how dangerous this behaviour could be, to his reputation and to his self esteem. He needs to know that its perfectly Ok to investigate his own body and how it feels, but never to involve someone else who doesnt understand whats happening. Above all, he mustn't feel like this makes him a bad person, and give him a hug and tell him you love him lots and that hes a great kid! (goes without saying i know, but its really important)
There is a lot more that could be said about this, if you want to email me, I'd be happy to try and give you some moral support.
