When I was younger my family stayed with another family we've known for years. When they came to our state they'd stay with us and vice versa.
We were there about two weeks during the summer. A boy about my age is who I'd play with. He had a sister a few years older.
We'd play mostly outside. Their yard was huge a few acres at least. The back was all grass and very few trees. When I had to pee I'd run to the house and use a half bath behind the garage.
I did this so many times I never even thought of knocking on the door as hardly any one else ever used that bathroom.
To get to it you had to walk through the laundry room so it was a room off another small room. When I would use it I'd unzip as soon as I walked into the laundry room. Turn a corner and I'd be in the half bath.
One day as usual I had unzipped and had pulled my cock out of my pants, made the turn and there is the older sister with her pants around her ankles and her bald pussy on display. I wasn't sure what to do because when I was walking in there were voices behind me so I knew I couldn't just walk back out without being seen by whom ever it was in the laundry room.
I turned to leave and then though better of it. I'd better zip up first. My penis wasn't going to comply as the visual scene before me made it hard.
At the time I didn't know anything about sex or masturbation. All I knew was that seeing a girl's pussy or thinking about them would get me hard.
This girl obviously knew a little more than I did. She reached out and pulled my hands from my zipper and gave me the universal sign to be quiet with a finger to her lips.
I just stood and stared at that hairless pussy slit. She gave my cock a little tug and it was sticking straight out my fly.
She put one hand to her pussy and started to masturbate. I had no idea what she was doing but watched intently. After a bit her whole body shuddered and went stiff.
As the voices that came from the laundry room had now gone she pulled up her pants, walked past me and left. I stood there awhile kind of in shock. My penis was not going to let me pee being at full erection. I pushed it in may pants and also walked out.
The rest of the stay I tried to keep tabs of where this girl was so maybe we could do it again. I just liked having a hard dick, I always felt good with an erection even though it would be a few more years before I learned what fun you could have with it.