When I was a kid I had two nieces who were my own age. In fact Denice was a few weeks older and Heidi was only about 18 months younger. We grew up in the same house because my sister, their mom was a real loser. She was on drugs and gone frequently. Well we were home alone a lot and got curious about sex and started with games like truth or dare and playing family. I was 12 when we started and this progressed to a "show mine if you show me yours" kinda game. We started touching each other and even did oral on each other. By the time I was 13 we were doing everything but sex. The summer I was 13 that all changed. It was a truth or dare game again and we had already dared each other to perform oral on one another when Denice dared Heidi to have sex with me. I was blown away when she agreed. She laid on the bed and took off her pants and panties. I did the same and and climbed on top of her. I had trouble getting it in at fist but she helped me and after a few minutes we were fucking. I looked over and Denice was watching and rubbing herself. Heidi was granting with every thrust and warned me not to leave any hickies. I kept pumping until I came inside of her. When I pulled out she said "wow that was a lot of fun" she then told Denice it was her turn. I had just came and wasn't hard so Heidi sucked me until I was hard again which didn't take long. Denice then climbed on the bed naked and said lets go. Having just done it I knew better this time and got it in her easily. We had sex for a longer time and Denice was more vocal than Heidi. I eventually came inside of her. She said that we will be doing that again soon. By the time we had finished it was almost time for the grown ups to come home so we cleaned up but after that we had sex as often as we could that summer until they moved away. We had sex a few times after they moved away as well and the last time Denice and I had sex I was about 17 and we had sex in her car. Heidi and I continued on even as adults. We would have sex if we were alone. This didn't happen often as we lived in different towns. But as luck would have it my work sent me to her town over the past weekend. We are both married but we couldn't resist each other. We had sex at least 4 times over the past weekend.