I was about 13 at the time and I was playing in the garden of my friend Mark. He had a younger sister Lorraine, who was about 12. Lorraine often tried to hang around with us and I could tell that she fancied me.
Whilst we were all playing in the garden having water fights, Mark's father took him off to some shop (can't remember why) and left me in charge of looking after Lorraine. We were both very wet and I noticed that Lorraines nipples were very hard and poking through her bathing suit. She saw me looking and asked me if I wanted to see them !
I said yes and we both went into the rear of her Dad's garage. there she slipped down her bathing suit and I looked closely at her small puffy breasts for the first time. They were only tiny, but they gave me a raging hard on. Lorraine noticed this and asked if she could see my willy. I felt a little awkward and at first refused. She said I could kiss her nipples and look at her privates if I got out my dick.
I agreed and pulled down my trunks. My dick was very hard and stuck straight up into the air. Lorraine said she had seen her brothers a lot and that she had often sucked on it. I was amazed and asked her if she liked doing it. She said yes and asked if I'd her to do it to me. I nodded and she knelt down and started to suck on my dick. This was the first time anyone had held my dick let alone suck it and it wasn't long before I came into her mouth. I expected her to be upset that I had cum in her mouth, but she just swallowed the lot and smiled.
She then asked me to kiss her nipples and pull down her bathing suit. I did as asked and sucked gently on her hard nipples. She began to rub her hairless pussy and after a while, she let me touch her pussy on the spot where she liked to be rubbed. I kept sucking her nipples and she soon started moaning and her pussy got very wet. She sort of held her breath and went very rigid. Then she suddenly grabbed me and kissed me very hard and shoved her tongue in my mouth whilst moaning loudly. I now know this was her Orgasm, but at the time I was a little scared and asked her what was wrong. She said nothing and that she had just cum and thanked me for giving her so much pleasure. I asked her if her brother did the same to her and she said yes almost every night.
We never did anything again like this again, but I have often wanked my self off whilst remembering this encounter.