Hi Goodsoulette. Long time no speak. I WOULD light heartedly speak to his Mum, I mean come on, YOU would want to know wouldnt you if it were your son.
My Tilly started to explore herself when she was first 10. We were on holiday and she said to me "I am just going into the bedroom for a rest, not to go to sleep, but just to rest" I had actually seen her in the bath that morning exploring herself. So........................I went into the bedroom, shut the curtains and said to her "it is okay to do that, but you REALLY dont want everyone looking through the window at you do you.
She now knows its okay to do it, but to do it in private.
You are right, it IS a very delicate subject but children are resiliant to the truth, it is us adults that get embarrassed. Just be honest and open as much as you can be in a child like way.
Katie. x