I sincerely hope uou aren't a parent , again 1st up on Google
http://www.askdrsears.com/topics/pa...sexuality/genital-play-whats-normal-whats-not
What to do. First, to compose yourself and resist the impulse to come on strong toward the children telling them that they have done something “dirty” or “bad.” Calmly and matter-of-factly introduce a new activity. (i.e., “Let’s go have a snack. I’ll help you get dressed.”) As soon as a private moment is possible (or right away if both children are yours) have a talk with your child. Convey that you are not angry. If children sense that they have done something bad or that you are angry, they will clam up. Tell your child that it’s normal to be curious about another’s body parts, and that you understand his curiosity, but that “its not right to touch anyone else’s private parts or let them touch yours. I want you to promise mommy that you will keep your private parts private and not touch anybody else’s.” Let the parents of the other child know how you handled the situation so they can do likewise.