My sister and i used to fuck all the time. Starting from when i was shown sex by a School friend at 6. I quick introduced my sister to the pleasures of self stimulation. From the you show me i'll show you stage it progressed right they way. we kept finding new things to do. Our parents had a hard time keeping clothes on us and eventually stopped caring. They were also sexual progressive and once they found out we had been having sex were not concerned at all. They set down the ground rules. We could have sex or play anytime we felt like it as long as the other person agreed. They also became a lot more open around that time. I can recall watching my mother sucking my dads cock while we were having family movie night. and walking in from school and seeing Mum naked with cum all over her body. Our most fun times were when we have friends over. Mum and dad turned in to the conservative parents at that point(unless the family were "Close Friends") but we'd have fun playing with our friends. My 8 year birthday party, my sister took on the entire group of 6 kids. She had a cock or tongue in every hole for about 60 minutes, When ever someone got tired wed swap around, at the end we had to put her to bed because she was so worn out. Pretty sure Mum and dad knew what was going on because they fucked so loudly that night i couldnt sleep.

Plenty of other stories but that will do for now