I was wondering what was the name of a chilhood movie of mines. I remember that there was a little boy who was afraid of monsters under his bed. Then he met one of those monsters and became best friends with him. The monster would take him to another world with him at night. The monster was not really that scary.

Here is Monsters, Inc is this the movie?

Monsters, Inc. (2001)

Little Monsters (1989)

Little monsters is the one you are thinking of.