I was in the park with my cousin and his next door neighbor, a girl. We were all about 12-13. The girl said she had to pee and we both said we did too. We all went in the girls side of the bathroom and watched her drop her shorts and panties to pee. She said it was only fair that she get to watch us so we dropped trou and let her watch us. After we all stood there with our pants around our ankles and exploring each others bodies a bit until an older came in and called the girl a slut and us perverts. We just left laughing. I have always wondered how far we would have went if not interupted.

I was 12 and my cousin was 8 she saw me naked in my room

I was 10. I was playing in the woods with the 10 year old girl who lived next door. I needed a pee and went behind a tree to do it. As I was peeing the girl sneaked around the tree & saw me peeing and of course she saw my penis. She took a good look at it and I said she could touch it. She gingerly touched it and as she did I began getting hard so I quickly put it back into my jeans.
She then asked if I wanted to see her fanny (UK word for pussy). I said I would so she lifted her skirt and pulled down her navy-blue cotton serge knickers. I just stared at it- her fanny that is. She let me touch it before she crouched down to pee letting me watch the whole time.