I used to believe that the Slestak (from the TV show "Land of the Lost") lived under my bed, and if I didn't sleep with my hands and feet under the blankets, they would cut them off and replace them with the weird crab-like claws they had.
A childhood belief about under my bed

others believed things like this
- I thought chicken's feet were witch's hands — Edward
- When I was a kid I always thought that a water tower was the robot from the TV show "Lost in Space".— sherryj
- I always had to sleep with my feet under the covers or else speed racer would drive over them.Anon
- I used to think that
"The land of make believe"
was
"The land of baked beans."— Baked Bean! - I used to believe that teachers lived in ufos at night and tha's why they dressed so weird.— llama queen
- When ever we went to the gas station, it was to replace the blinker fluid.Anon