I used to believe when I was about 3 or 4 in 1950, that there were a population of tiny people made of paper called "The Saturdays". They were triangular shaped and lived on a night-shift basis. When they went to bed at dawn, they would hang themselves up on the nails in a vertically stored "Bagatelle Board" kept in a cupboard under the stairs.
I don't think the bagatelle board was ever in use and we never went into that cupboard by day as it was dark and there were Saturdays in there asleep.
My parents told me I really did believe they lived in there and came out when I was asleep.
A childhood belief about imaginary friends

others believed things like this
- I used to think that panthers lived in our cupboard.— entertainer
- I used to think that in public toilets, the cleaning lady actually lived in the supply cupboard.Anon
- I used to believe that a weegie board was some sort of surf board.— Missa
- I used to believe that tv people were tiny famous people that lived inside that box with a window called TV.— Miguel Horacio
- I used to think that a clown lived under my bed and tried to eat me while i was asleepAnon
- I used to believe that boarding school was where people went to play board games.Anon