This is NSFW. I've never told this to a single soul. I should really be using a throwaway for this and this probably deserves to be on r/offmychest instead of here. However, because none of my comments on any r/AskRedditpost has ever been viewed by anyone because I'm late to every post, I'll keep it here unless I decide to remove it later on.
When I was young, between the ages of 8-10, and I would stay over at a relatives house (grandparents, aunt/uncle's even my own) with my female cousin, a year older than me, we would "pretend" to have sex.
What I mean by this is, if it were just her and I in a bedroom, we'd turn off the lights and "play" this "game" we made up. It usually involved her pretending to be a guy, me a girl with a penis, and we would pretty much pretend to have sex. It wasn't sex, mind you, considering there was no penetration or ejaculation (this was before I really knew what sex or masturbation even was) and she was never naked. I also never made anything up, she would always tell me to do things and I would do them (get naked and things like that). All that happened was she would kind of hump my leg for a little while and that would really be it. The thing is, sometimes her younger brother would walk into the room, and because it was always pitch black with the lights turned off and all and because we were under the covers, and because she'd always be on top of me when we were doing it, she'd quickly roll over before he could see what was going on. If anyone walked in on us and recognized that she was on top of me while I was usually completely naked, there would be absolutely no explanation. We wouldn't say we were having sex because we weren't, just kind of playfully touching, so there would be no real way to explain exactly what the fuck it was we were doing.