3 Year Old Touching Inappropriately?

Sounds like he may be a victim of ual abuse himself.. Kids just dont "know" how to do these things, something may have happened to him (or still is) and he is just re-enacting the behavior. Either that, or he's been in situations where he's seen this before. Either way, the child doesnt need to be around your daughter alone anymore.. Regardless if your just leaving the room for two seconds to get something, pick her up and take her with you. Its not the boys fault, but he cant be trusted alone