Family Fun at a Reunion

This happened about 6mos. ago.I was in Ca.at a family reunion.We all decided to go to a park for a picnic.We didn't have enough room so.my niece had to sit on my lap.She is always wearing short shorts and halter top and has about a 40DD.I was in the back seat when she came in a sat on my lap.I had gotten a hard on just seeing her before sat on my lap.She saw my hard on as she was getting in and just smiled.She sat n my lap and let out a little moan.She was leaning forward talking to the people in the front seat.She started sliding back and forth on my rock hard cock as she was talking.I couldn't believe she was doing this but,I wasn't about to stop her.She took my hand and put it on her pussy and started my hand rubbing up and down.I don't know how she could contol her self so well but,no one in the front seat could tell anything was going on.We went on about 15min. like this then when the front of her pants started getting wet.I was going crazy.I started cumming in my pants.In about 5min. she was cumming also.We finnaly reached the park and I had to stay in the car about 5min or so after she left so I could clean upI get a hardon now just thing about it.I have more to the story I will tell later