It's awfully hard being in the middle, my older brother was always taller and stronger than me, while my younger sister was always my parent's favourite and she had all the brains too. I was stuck in the middle with nothing. Well not quite nothing for I had all the sporting talent, if there was a ball involved I could hit it. So a couple of times a week I would stay behind after school for some practice or other. This night it was raining hard and cricket nets had been cancelled so I walked home alone for my sister and brother had departed some minutes earlier.

I used my key to get in and threw my kit down in the hall. Suddenly I could hear noises upstairs. Ok I knew my siblings must already be home but this was more, more like a moan. As silently as possible I sneaked upstairs and stood beside my sister's bedroom door. It wasn't quite closed but I still couldn't see inside but I could hear her. I reached out and pushed the door slightly so I could see into the room. There on the bed was Lucy with Barry moving on top of her. At first I didn't understand what I was seeing then it struck me; he was fucking her. Sure I had the sex education lectures but I never expected to actually see it live.

Lucy was still fully dressed as far as I could see while Barry had his trousers half way down his thighs. Just then Lucy turned her head and I could see her eyes widen as she spotted me in the doorway. She didn't do anything else but stare straight at me while Barry still thrust into her. A few more minutes and Barry was winding up for his climax and then after three twitches he was still.

I moved away and went to my own room and sat on the bed. It was typical for me to be left out of anything that my brother and sister did. After a few minutes I hear movement and I suppose Barry went back to his room to start his homework.

"Can I came in?" asked Lucy her head around my door.

"Sure," I replied.

"You're in early," she smiled, "we didn't expect you for some time."

"Yeah, nets cancelled because of the rain," I explained.

"Oh, I see," she said.

She sat down beside me and we didn't speak for some time.

"You mustn't say anything about what you saw earlier," she said at last, "you would get us in trouble if you did."

"Yeah, no problem," I said but of course there was.

"It just it so nice when we do it," she explained, "there's no harm in it, just a little fun."

"Yes I see," I said.

"You're too young to understand just yet," she went on.

"But you're younger than me," I said.

"Yeah, but girls grow up faster than boys," she explained.

"So when I'm older I can do that to you too?" I asked.

"Do you want to?" she asked.

I didn't answer but just nodded.

"Ok, we'll see," she said and giggled, her hand resting on my thigh.

She left then and I started on my homework.

I thought about what I had seen over the next few days and especially about my sister. She was still a little scrawny, not like Alice Truman in my class whose tits are quite large and all the guys go goggle eyed whenever she walked passed. No her tits are barely discernable under her school blouse and her legs were a little thin. Each night, in my mind I would see again Barry moving between her legs and my cock would get hard and I would rub it until I spunked into a tissue.

"Where's Barry?" I asked Lucy.

It was a week later and when I came home Lucy was in on her own.

"Oh he's in detention," she laughed.

"Can I come in then?" I said softly.

"Sure," she said looking up at me from where she sat on her bed.

"I'm older than I was last week," I said boldly.

"So," she giggled.

"So I want to do it to you just like Barry does," I said.

"So you think you're old enough then," she said.

"Yes," I said proudly, "my cock gets hard every night."

"If I let you, you must promise not to tell anybody, ok," she said.

"Sure," I said.

"No I mean it," she said again, "you must not tell anybody, not Barry, not your friends at school, nobody."

"Yeah I understand," I said.

"Well ok," she said with a strange tone to her voice.

She reached under her short school skirt and pulled down her knickers, then she lay down on her bed and opened her legs wide.

"Come here then," she called.

I climbed onto her bed and knelt between her spread thighs.

"Here let me," she said sitting up and undoing my belt and pulling my trousers down.

"Mmm that's quite nice," she said her hands holding my stiff cock.

"Right let me," she said and she positioned me in the right place and pushed down onto me.

"Oh yes," she sighed, "that is so nice. Please just move a bit."

I pushed forward slightly and her hips pushed back at me.

"Yes, that's it," she sighed, "now do it harder."

Following her instructions I pushed in and out of her while she pushed back at me.

"Oh God yes," she said her arms going around my neck and hugging me tight, "just a bit longer please."

I could feel my spunk rising but I carried on moving on top of her until she squealed out. For the first time in my short life I pumped my spunk into the body of a girl.

I lay on top of her for some time, then I felt my soft cock plop out of her.

"You can get off now," she said sweetly.

"Sorry," I said getting up and pulling up my trousers.

She pulled down her skirt but not before I saw a flash of her pussy.

"Thank you," she said, "that was very nice."

"Yes it was," I confirmed, "can we do it again sometime?"

"Sure," she said with a smile, "when we are alone. Now remember what I said, tell no one, ok."

"Sure sis," I said.

"Now we better get on with our homework," she said pulling on her knickers.

Barry came in a few minutes later and I could hear her bed springs going again as he took his turn. I suddenly felt a flash of jealousy but I knew it was silly for me to think like that, but I still did.

I didn't like it but Barry still had the inside track with her, all the while I was away from home leaving them together I just knew he was humping her; my game suffered a lot that year. About once a mouth she would call me into her room when Barry wasn't around and asked me if I wanted a go. She would then slip off her school knickers and spread her legs for me.

Things stayed much the same for a while then things started to happen. I hadn't notice it at first but once when I was pumping between her legs I felt her tits up against my chest and my how they had grown. When I had finished and before she smoothed her skirt down I also noticed that her legs were no longer scrawny but they had filled out too. The final conformation came when we went on holiday soon after and she wore a bikini for the first time. I couldn't believe what I was seeing, suddenly she was no longer that thin little girl but now she was very curvy and sexy.

Not once in all the times we had done it together had she removed anything more than her knickers or allowed me to touch her, but now that I had seen her figure in her swimming costume I wanted to more than ever.