Little Monsters

Little Monsters is a movie starring Fred Savage, Howie Mandel, and Daniel Stern. A boy discovers an incredible and gruesome world of monsters under his bed.
A young boy is scared of the monster under his bed. He asks his 6th grade brother to swap rooms for the night as a bet that the monster really exists. Soon the brother becomes friends with the monster and discovers a whole new world of fun and games under his bed where pulling pranks on kids and other monsters is the main attraction.