My older brother told me that when girls are born their testicles migrate up to their sides. That's why they don't like it when you pinch/tickle them there.
A childhood belief about rude bits

others believed things like this
- I used to believe that I was older than my brother because I was born in June and he was born in OctoberAnon
- I used to think that my testicles were eggs that would become babies when I was older...— Martin
- i used to think boys were born from men and girls were born from women— swag lad123
- i believe that if im born in december im older then people born in may— runawayfox16
- My brother told me that I would turn into a boy when I got older. It made me cry.— Sarah
- I used to eat doggy chocs until my older brother told me that if I did I would have puppies.— EG