This happened this summer.
This happened when I was a 17 year old high school girl and I often babysat for a couple who work with my dad.
Every couple of months they would go out for a 'date night' and spend the night in a motel, returning the next morning. They paid me $50 to look after their four year old daughter overnight, it is a great deal. Like most girls I assume I masturbate several times a week. I liked to masturbate when I babysit because I know there is nobody in the house, except the little girl and me. I was still a virgin.
One of first times I babysat, I spoke to the wife when I was waiting to be picked up by my sister. She mentioned that they had been to the motel that night. When I was driving home, I asked my sister why they would go to a motel after dinner instead of coming home. My sister laughed so hard she had to stop the car. She said 'so they can make love'. It had not even entered my mind.
Each time I babysat after that time I always got turned on by the thought of the couple making love all night. I would take my clothes off and watch TV nude, while rubbing my clit to a great orgasm. I can only have one most times, so afterwards I get into my pjs and sleep on the couch. Sometimes the couple comes home at 4 AM and I get the baby up and let them sleep in.
The best time was once when I found a used condom in the bathroom trashcan. It was the first used condom I had ever seen. When I picked it up and squeezed the sac on the tip some fluid came out, and I smelled it. I got very hot thinking that it had been inside the wife and covering his cock. As I was thinking this I realized I had put my hand in my pants and was fingering myself. I quickly came in a very strong orgasm right there on the bathroom floor. The best I had ever had.
Months later I started snooping through some drawers in the master bedroom and found where they keep the condoms, lube, and a vibrator. The vibrator was blue and shaped like an 'L'. I did not touch anything, but I could not get the vibrator out of my mind.
The next time I babysat I made the girl go to bed early and I got the vibrator out of the drawer. I did not know what to do so I just rubbed it on my crotch through my panties. As I got wetter, I started rubbing it onto my vagina and clit. I tried to put it inside me but it was too big at first. It took some time, but I got it inside. The feeling was incredible, kind of painful, but still good. I started working it deeper by sitting up on a couch pillow and riding it. Just as I was coming the little girl walked into the room and asked for a drink of water. I freaked out, I was so scared she was going to say something, but she did not seem to take any notice to what I was doing. I could not get the vibe out so I waddled into the kitchen with it still inside me to get her a drink.
Afterward I went into the bathroom and pulled it out, washed it and put it back where it belonged.