I used to believe that my mom had me and that my dad had my little brother... (we are just a year apart - I was very young...) boys have boys and girls have girls...
A childhood belief about reproduction

others believed things like this
- I thought that the difference between girls and boys was that girls have teeth.
Anon - I used to believe all babies came out as girls and later on in life some of those girls turned into boys — Tom
- I used to believe that boys, gave birth to boys and girls gave birth to girls. How i'm so wrong now.— Sarah
- I used to believe that little boys grew up to be girls and little girls grew up to be boys. — Darin
- when I was a kid, I used to believe that only girls could be my friends and all other boys were my brothers.
— rajat - I used to believe that tigers were girls and lions were boys— Ruth