He’s probably masturbating while looking and touching these items, but it probably won’t turn into anything serious once he’s old enough to get a girl friend. However, I would be a little careful about walking around in front of him in a state of undress. Just try to be as modest around him as possible. And if you or your husband hasn’t had “the talk” with him, them it’s probably time. If it hasn’t happened, then I would suggest that your husband handle it. Get him an age appropriate book too. (I would say that my book, Sex For Dummies would be OK for a boy his age but of course you could get him some other book too.) Make sure he knows that you’re both there to answer any questions he might have. And you might consider having your husband give him a copy of Playboy. That way he would have some material to masturbate to that would be more appropriate than his mother’s underwear.