I used to believe that as people got older, they changed into the opposite sex. I don't know why, but I always associated this thought with a Hershey Chocolate commercial I saw when I was a kid.
A childhood belief about getting older

others believed things like this
- my dad told me that hershey park was made completely out of chocolateAnon
- i used to believe that everyone was born as the opposite sex, and that you changed when you started school.— llama
- I thought that little tiny people changed the color of the stop lights.Anon
- I used to believe that black people were white people dipped in Chocolate. That's what my dad told me...— Steve
- Chocolate, they say, rots your teeth. I believed if you drank chocolate milk, your bones would be brown.— Dellio
- I used to belive chocolate milk came from brown or chocolate cows.Anon