This happened when I was 14 and the neighbor's sister was about 11 or 12.
I went to my friend joe's house to see if he wanted to play some football but when I arrived no one was home except his little sister Sherri. Sherri said everyone except her had left for the mall and wouldn't be back for about two or three hours. I asked Sherri to have Joe call me when he got home. I then asked Sherri if I could use the bathroom before I left since it would take me about 30 minutes to walk home. She said ok and led me to the bath room where I went in and closed the door and took out my cock and took a leak. As I was peeing I looked over and the bathroom door was partly opened and Sherri was staring at the pee coming from my cock. I tried to pull my pants up by Sherri reached out and took hold of my cock and said she had never seen one before. As she was holding it began to get hard and this seemed to excite her even more. I told her she shouldn't be touching me there but she kept holding and staring at my 4-inch manhood. As she continued to touch my cock and since this was the first time I had ever had a girl touch me there I started to move around because it felt so good and then I started to shoot cum. This amazed her even more and she took her hand off my cock. I told her that is what happens with boys and I asked if I could see her privates since she had seen me. She jumped up and quickly removed her shirt, pants and under pants the opened her legs for me to see my first real slit. Her slit was slightly covered with wisps of brown pubic hair. Her breasts were not much more than erect nipples slightly raised from here chest. I reached out and fondled her slit, rubbing my fingers along her pubes and kissing her nipples. She grasped my cock which was hard again and started to jerk it like before and I came again. We would continue to learn more about our bodies over the next six months until her family moved out of state.