This happened a year ago three days after my birthday, she was 10 and I was 14.
One extremely hot evening in August, I decided to sleep in the nude because our air conditioning didn't work. So I got in to bed, I slept great through the night, then was woken up by my little sister Tiffany who jumped in to my bed and scared the hell out of me!
She said 'Wow you're naked!' I said 'Yes I know, could you give me some privacy?' 'Ok' she replied. She walked away kind of sad, I guess she liked looking at me, since she had never seen a 'Grown Up' girl before. 'Actually, Tiffany, come here'. I saw her face light up as she jumped back into my bed. I asked her if she had ever masturbated and if she knew what it was. She said she hadn't and I told her I would teach her how too. She asked me what it was. I told her it was something you could do that made you feel really good. She smiled at the idea.
'First you have to take off your pants and underwear,' I said. She giggled, but she did it just like I had told her she had too. I told her if she took off her shirt it would be more fun, so she did and we were both completely naked in my bed in my room.
I said 'Take your fingers and move it up and down your pussy.' 'What's a pussy?' she asked. I told her it was where she goes to pee, and where you have babies. She laughed at the thought of that, since she was only ten and still hadn't taken sex ed in school. I put my fingers on my pussy that was already wet with excitement and began to move them up and down my clit and then told her to do the same to herself. She did, and I heard her groaning softly. I could tell that she loved it. Her eyes fluttered up and down. 'Now while your doing this you can move your hands all around your body and pinch your nipples, and once you get to your boobs, you can play with those'. 'Ohh ok... cool! Wow this feels really good Liz' she screamed.
I could tell she was reaching orgasm because she began to yell very loudly. It was a good thing that nobody was home otherwise my parents would have caught us, not that they would have cared, it just would have been awkward. She yelled extremely loud and laughed and started to hug me and thanked me for showing her such an awesome thing. 'Thank you so much big sis, How many times do you do this?' she asked. 'Oh about twice a day, but you are allowed to do it as many times as you want'.
Since this day, she masturbates at least twice a day, I know because I can often hear her. Sometimes we do it together, like we did that day when I taught my little sister.