4 year old humping 3 year old?

I don't think this is such an odd thing, and probably isn't always caused by sexual abuse or exposure. In my opinion it is kind of normal unless it continues for a long time or seems to be a big problem for the child. In my years of day care I've had several young children that have done this. Boys and girls. My kids did it too, but not to the degree of some of the others I cared for. One little girl eventually rubbed the fabric off the arm of a chair doing it. One little boy tortured us all for weeks with his little willie, he got bored with it soon enough. I always stopped them when I saw it, just as if they were doing something like, biting, hitting, picking their nose, not sharing, or peeing in the corner, toy box or the trash can cause you might miss something if you go to the bathroom! I always told them it's just not something you do in front of other people or to other people. If you are a dog it's ok, that is what dogs do, but even the dogs get a reprimand if they do it in front of me! It's not sexual to them I don't think, most kids don't understand sex enough. It just feels good and they are learning about their bodies. Masturbation is natural and nothing to be ashamed of, but just like sex, we need to be taught when and where to do it. I wouldn't make a big deal out of it with her, it will pass, and if it doesn't then it could be time to worry. I would try and evaluate why you feel so disgusted by her actions. And I am curious/confused as to why your husband couldn't handle it and needed to call you to come home and deal with it. Has it become that big of a problem? Wishing for you patience and the right words and understanding to deal with it all. Hang in there Mom :)