When I was a little kid I used to believe that as people grew up, their bodies didn't grow but an older version of them just grew around the younger version like a shell and that person would take over. There were different stages as you grew up and I though that when I was a teenager I'd be trapped inside some teenage guy's body, and then later we would both be trapped inside an adult body..and so on.
Funny thing was, when I explained this to my Grandma at the age of five she understood it! I remember she made a joke and said, "My God, I must have a ton of people trapped inside me."
A childhood belief about getting older

others believed things like this
- I used to believe the Metallica song "Trapped Under Ice" said "I turned down the rice."— Erik Z.
- I used to think that when you died, you would be awake trapped in your coffin rotting for all eternity!— Trapped in the Coffin
- I used to believe people grew from spores and when we got old, we'd grow leaves and flowers etc— Calvin (from my pet tiger Hobbes)
- I used to think that bodily tissues were kleenex sheets that grew in certain parts of your body.Anon
- I used to believe in the 'little men' that worked inside your body.Anon
- I used to believe that when there was static on the tv, it would be showing the inside of your body.— Dr.Starr2.0