I used to think that Ford Anglia cars were made by Heinz. This was because the oddly sloping rear window, when seen from the side, closely resembled the shape of the panel on a Heinz label.
To this day, if I see a Ford Anglia or a picture of one, I say "that's a Heinz Baked Beans car."
A childhood belief about cars

others believed things like this
- That baked beans were made of pasta! Spaghetti is?!Anon
- I used to believe that President Ford invented the automobile.Anon
- My mum used to tell me that baked beans were just peas covered in tomato sauce.— munky
- I used to think that
"The land of make believe"
was
"The land of baked beans."— Baked Bean! - I used to believe that the oddly-shaped clouds were made from oddly-shaped sheep— Dickson
- I used to think that little bakers lived in the toaster who baked the bread and pushed it back up.— Karen K