This is such a good topic I thought I would add my early experience. Along with having my rectal temperature taken, this is one of my earliest memories and is probably one of the primary reasons I love anything anal. When I was about 4 or 5 years old I remember being home with my mother and the lady from next door was visiting. We were very close to the family next door and the woman was like a second mother to us. Although I didn't know the name for it I was constipated and told my mother that I needed to poop but nothing would come out. What a mistake that was! At this point in my life I had no idea what a suppository or enema was.
I remember being out of sorts and complaining about it several times to my mother, who was sitting at our dining room table talking to the neighbor lady. I guess she finally had enough of my complaining because the next thing I knew she had asked me to come over to her. She then told me she was going to give me something to help. She pulled down my shorts and underwear and picked me up and set me down on the edge of the table. I was completely embarrassed and scared with the neighbor sitting right there. I thought I was going to have my temperature taken and started to say no and resist. My mother had other thoughts and quickly grabbed my ankles and leaned me back so I was laying on my back with my legs up in the air and my bum completely exposed. I caught a glimpse of a white stick and I realized it wasn't a thermometer. (It was one of those long thin suppositories that were used on children back when i was young.) She immediately pushed the suppository deep into my rectum. I remember it seemed like it was going in forever, much further than the rectal thermometer I had experienced in the past, and I was crying inconsolably.
It all happened so quickly that I still wasn't sure what was going on when she sat me up and lifted me back on the floor and pulled up my pants. I knew there was still something in my bum and I pleaded with her to take it out but she said she couldn't since she had pushed it all the way inside. This just made me panic even more as I was unfamiliar with what a suppository did and just assumed there was no way to get it out. I still pleaded with her to take it out but she just said it would help me to poop.
After that I just went away sobbing to my room, still being tortured by the thing my mom had irretrievably shoved up my bum. It wasn't much later that I figured I should try to poop again and out came a large poop with the partially melted suppository. This was the only time I ever got a suppository as a kid. I don't really remember being constipated in my youth but if I was I'm sure I never mentioned it to my mother again. It's funny how these childhood events help create our fetishes later in life, not that I'm complaining.