I can recall psychology classes in child development and children will often be very vocal or expressive when they first discover "private parts" Many times, parents get condemned for a child's naturally expressed fascination with the anatomy.

If there is concern about other evidence on the body of possible abuse notify authorities. If this is solely based on that behaviour, I would say be cautious about allowing the child over and even videotaping a visit if both parents are around and the child comes to visit.

A consultation with a lawyer might be of interest due to paranoia in our society rather than because of the child.

That is my two cents worth.