When I was a fairly little kid, I thought that people grew up and then they grew down again. My very old great-grandmother was quite short, because she had a bent back, and she was never super-tall to begin with, so my parents and even my grandma towered over her. I assumed you started out small, and ended up small again.
A childhood belief about getting older

others believed things like this
- I thought small cars grew up to become big cars— carhugger
- when I was small I always thought that the solar system ended, and then it was just white paper after that— sparrow
- That everyone had the same amount of skin and that short people were fat and tall people were skinny.Anon
- i used to think a small man named homer lived in my grandmother's freezer and made ice. — ana
- I thought plants only grew when people were not looking at them.Anon
- When I was small I thought people were actually inside the TV and that we could take them out.Anon