My parents hired a babysitter to look after me on the weekends when they went out.
I knew nothing about sex and being an only child did not have the benefit of a sister to give me even the most basic understanding of the differences between boys and girls. It just had not yet entered my mind.
The first night the babysitter was there I got into the bathtub as usual and she came in and was sitting on the side of the tub washing me. At some point she reached down and began to squeeze, caress and stroke my penis. I was fascinated as it grew hard and enjoyed the feelings. The babysitter got me to lay down in the tub and quickly stroked me off.
We would do this every time she came over for the next several years. I had begun to move into puberty and was much taller than before. Although my penis had developed I had not started to eject sperm yet. I remember the first time I did, a small pea-sized drop of semen appeared on the tip of my penis after I had orgasmed. The babysitter did not notice. The next time I clearly shot sperm into the air and that was the end of our bathtub fun. She never did it to me again saying that I could now get her pregnant. I was very disappointed. Up to this day I had never masturbated myself and did not know that I could do it to myself.
Later that year in school we had a sex ed class and the teacher talked to us about self-pleasure - it was like a light-bulb had gone on. I understood and from that day I masturbated daily.