DD is 3.5 and her cousin is 5 just started school. The last couple of play dates we have had, they have ended up taking off their clothes and showing each other private parts. The first time we walked in on him on top of her and so have avoided seeing them for about a month but today on the first play date since, we walked in on her pulling up her trousers again. When questioned she says that he asks to see it and shows her his too and that they are playing mummy's and daddy's but tells her to keep it a secret. We have spoken a lot about private parts and that she should not show anyone and that it is hers etc etc and if he asks again that she needs to say no and tell mama and daddy but I still feel very uneasy that it has happened the moment we have met up again. We are close family living only 5 mins away and so it's inevitable that they will see each other and play without supervision. I know that at this age things are innocent and I don't want to make a big deal out of something that I shouldn't be but at the same time there's a little voice in my head that just feels uncomfortable and not I'm sure how else to deal with it?