Oh, oh. He has been peeking in on adult love-making. Of course you have to explain that this is not correct behavior, but also find out who among the adults is being careless.
Hi Gutz, now is the time to have a sit down talk with your wife about this. It seems that you have raised your daughter with some values that are different from your step son. You need to find out who is exposing him to this type of information. They should be living all the child hood things that we were exposed to. To me this type of sexual behavior from your step son is out of character for that age. I believe a child can have their own sexual fantacies but bringing other children into this fantacy, to me is inappropiate.