Well, for me it started with my sister. I was very young at the time so I didn't have any idea what was going on, when I walked into the barn and heard grunting from one of the stallions. I walked into the stall to see what my sister was under the stallion and he was trying to shove his peepee into her.
When she saw me she said something to the effect "shhhhhhhh, don't tell mom or dad and come give me a hand". SO I went over and she told me to guide his peepee into the hole that her pee came out of. I did not understand why at the age, but mom was always telling me to do what my sister told me so I did.
She had me do the same thing with the other 5 stallions in the barn. She said this is what we had to do as part of our daily chores when we got home from school from now on, but we had to be done before mom and dad got home, and I could never tell mom and day because they were not to know who got the work done.
This continued to be our daily after school chores until I started to get old enough that I realized what was happening.
I made the mistake one day of telling mom when I got mad at my sister. Our mom about killed us. Not for the reason you might think. She was mad because for years she had been going out after we kids had gone to bed and she had been having fun with the stallions wile dad had fun with the mares. Turns out that since my sister had been relieving the stallions of their sexual desires earlier in the day, they did not have anything left for our mom at night.
Well, from that point on we all only went out after dark but before bed. My mom and sister helped each other take turns with the stallions while dad and I each chose our mare for the night. This went on until my sister and I both left for college. I assume mom and dad continued but sis and I ended up getting our own places and our own horses.