A lot of people think incest play is this OMG weird thing, but it's actually a natural and healthy thing that kids do all over the world. Only in the West do you find this sort of insane, stupid taboo about it.
I fondly remember, many years ago, having an experience with my cousin. I was going tinkle during a thanksgiving dinner at my Uncle's house and she walked in.
She pointed at my little tallywhacker and asked what it was. I told her it was my pee-pee, and she thought it was so interesting. I asked to she hers and she showed me her bare little muff. She started playing with my tiny pecker for a bit and I touched her back, exploring.
This was a totally natural thing, and we were just exploring each other. I wasn't "traumatized" or any of that stupid shit people claim can happen. I actually remember it fondly as an amazing thing. My cousin was probably 6 or 7 at the time and I was 38.:D