Thanks to a mix of the series V and an Star Wars action figure (that I still have!), I used to believe that each night an alien with tentacles hanging from his mouth would appear next to my bed. I would lie on my stomach and bend my knees so my feet were up, which would create a bulge in my sheets that was actually supposed to be an alien spy that was reporting on what I'd been up to. The tentacle-mouth alien would talk further with the spy, not knowing the spy was really me.
A childhood belief about under my bed

others believed things like this
- I thought the ball-headed person in the Bic logo was an alien and communicated using alien-like noises.Anon
- Oh oh, I'm an alien, I'm a little alien...
Legal maybe?— Marina - I used to think that my cat was an alien that had come to teach me how to be good!— laz
- I used to belive that my teacher was a alien unfortunately this was true mum and said. — peter
- I used to think that green poop ment you were an alien.— fartcheeks
- When I was little I used to believe that God looked like the Great Gazoo (the alien from "The Flintstones").— Susan