4 1/2 boys's sexual?? behavior

I have a 4 1/2 year old son (and a 1 year old son).  On three occasions my 4 1/2 year old son has layed on the floor and asked a 3 year old girl to lay on top of him.  This has happened at the babysitter's (who is like family.)  My son goes to preschool 3 days a week and to the babysitter two days a week.  The babysitter has brought this to my attention and asked how she should respond.  On the previous occasions she has just told both of them to quit it and go do something else, very nonchalantly.  The 3 year old girl cooperates when my son asks her to lay on top of him, which we see as unusual since they both seem to be annoyed with each other normally.  We are not sure if we should downplay the situation or if I should discuss this with him.  There are two other girls at the babysitters of approximately 2 years of age, a 3 year old boy and occasionally a 5 year old boy.  To the best of my knowledge, my son has never seen anyone in this position or seen it on T.V.  Other than this, my son is a typical 4 1/2 year old who is always concerned about how he appears to others.  How should we handle this situation?

[Kevin Kennedy, Ph.D.]

Dear Kathy,

I think all you need to do is set the limit and adhere to it. Simply tell your son that this sort of physical contact is not allowed. It's not clear where the idea may be coming from - you might ask your son and see what, if anything, you learn about it.

[hntrsmm]

A related discussion, sexual behavior in a 4 year old was started.