My siblings and I used to believe...
...that broccoli and cauliflower were actually little trees.
...that the "beans" in the middle of green beans were sleeping pills. [I have NO idea where we got that idea!]
...that it was possible to eat so much that you'd become full all the way to the top of your skull. We all claimed to have reached this state on many occasions.
A childhood belief about general

others believed things like this
- I used to think people were called "human beans".— Dave
- I used to call the rays of light from the sun "sun BEANS". That's what it sounded like to me.Anon
- That baked beans were made of pasta! Spaghetti is?!Anon
- My mum used to tell me that baked beans were just peas covered in tomato sauce.— munky
- Until just a few seconds ago, I thought gherkins were beans or something weird like natto...Anon
- I used to believe that broccoli were small trees Anon