Step-son iniating sex acts on my daughter

  I have a 8- year old step son that comes to stay with myself, his dad and my two children which are his brother and sister.  My daughter is 4 and my son is 6 months.  This particular night in question they were very quiet so I tip-toed to my daughters room to see what was going on.  When I entered the room I found my step son and my daughter under the covers. My step-son was on top of daughter with his underwear off and his private part by her mouth. He was looking down at her and was holding her head as if to guide her towrds his private part.  Her underwear was off as well.  After seeing this I was visibly shaken up by it and very upset. I sat my daughter down and spoke with her about her actions and I had my fiancee speak with his son about his actions. Upon speaking with my daughter my major concerns was what happened? What did he do ? What did she do? How often has this happened? She told me that he had put his private in her mouth and that it had never happened before and that he told her that they were going to play a game and that if she did not play this game with him that he would not play with her anymore.  I explained to her that behavior is wrong and it will not be tolerated.  My question is what should I do? I do not feel comfortable with my step-son being around my daughter anymore because according to what she told me it was forced upon her she only did it because he said that it was a game and that he would not play with her anymore.  As far as where he got this from he is not saying. We do have parental blocks on all tvs in the house, we do have parental blocks on the computer and they are not allowed on the computer without adult supervision, we do not exhibit any explicit behavior in front of the kids. I really do not want him to come back over to spend nights am I being too extreme when I say this?  Is their a better way of handling this?

[Kevin Kennedy, Ph.D.]

The behavior of course was wrong, but to reject your stepson is not going to be helpful. His father and mother should join forces and be sure he receives some professional help. This sort of behavior does not occur spontaneously with children. It will be important for all of you to work together to figure out what occurred, to figure out where he observed this or, even, if he has been victimized in some fashion. It is a natural instinct to protect our children, so your impulse to banish your stepson is understandable. But it is not humane. You can be more helpful by trying to address what occurred. Something very wrong happended with him to bring this about.