Sister and i unknowingly did roleplay
I am female, and I have a younger sister. When I was maybe 9 or 10 years old and she was 4 or 5, we'd share a bed at night.
Sometimes, we'd start to engage in a sort of roleplay, where we would "punish" each other through slapping, hairpulling, etc. We found it fun.
Back then, neither of us knew a thing about anything sexual. Now that I look back, I know I got some sort of sexual gratification out of it. I don't know about her, and I don't want to ask.
Many years have passed since, and besides those roleplays, we've had a very normal sibling relationship.