A horror movie called It’s Alive. I was 5 years old. My mom would rent horror movies without checking the ratings and I’d watch them. Even after this I always loved horror and never had nightmares or anything. But, I rewatched It’s Alive a few years ago and it is definitely not for kids…
But honestly the craziest thing my mom rented was The Toxic Avenger, when I was maybe 10. She never saw it herself it so still has no idea what she allowed me to watch at a young age!