Little Monsters is a 1989 American comedy film starring Fred Savage and Howie Mandel and directed by Richard Alan Greenberg. It tells the story of a boy who befriends a real-life "monster under the bed" and discovers a secret world of monsters who sneak into children's bedrooms at night to pull pranks on them.

Brian Stevenson, a 11-year-old boy and his family has just moved to suburban Boston, and he feels isolated in his new neighborhood. One morning, Brian finds himself blamed and wrongfully punished for several things he did not do. Insisting on his innocence, he blames his 8-year-old younger brother, Eric, who claims to have seen a monster the night before. At school, Brian gets into a fight with bully Ronnie Coleman. That night, upon returning to Eric's room to sleep for a bet, Brian finds the room in shambles, and sees the TV remote supernaturally slide and disappear under the bed. The next morning, Eric and his friend Todd find Brian on the living room couch and joke about Brian being unable to sleep the entire night in Eric's room. Brian bets Eric "double or nothing" to sleep in Eric's room another night. The next night, a determined Brian sets booby traps, and leaves cheese Doritos as bait to attract the alleged "monster."

Brian succeeds in trapping the monster intruder: a blue-skinned humanoid named Maurice. Though initially scared, Brian soon discovers that he and Maurice share the same interests and befriends him. Brian also learns that sunlight causes the monsters to collapse into piles of clothes. Over several nights, Maurice shows him a fun time in the monster world beneath Eric's bed. It consists of every child's dream: all the junk food and video games available, with no adults to supervise. It also has innumerable staircases leading to the spaces beneath children's beds, from which the monsters cause trouble. Maurice and Brian have fun making mischief in other people's homes, and Brian also befriends a girl named Kiersten at his school. However, at the same time, Brian also begins to notice Maurice's ways of causing mischief can go too far sometimes, as evidenced when Maurice eats Kiersten's papers for an important science project she was working on, causing her to get a grade of zero. Brian also becomes disheartened when he believes that his parents may possibly get a divorce.

One night, Maurice brings Brian along with several other monsters to the bedroom of an infant baby, intending to scare it. Finding this to be cruel, Brian opens the bedroom door, exposing the hallway light to the baby's bedroom, but subsequently learns that he is turning into a monster, as his body parts shrink when the light hits him. He escapes the house through the front door and walks through Todd's backyard, where Todd is sleeping in a treehouse. Todd shines a flashlight on Brian, shrinking Brian's arm in the process. The concerned Brian saws off the legs of all the beds in his house.

Due to Maurice's failure to convert Brian (all monsters are former children), Eric is kidnapped by Snik — another, much crueler monster — through the couch bed in the living room. Brian enlists help from Todd and Kiersten. Gathering an assortment of bright lights, they enter the monster universe looking for Eric. "Zapping" various monsters along the way, they march to the master staircase, where Boy, the ruler of the monster world, resides. Boy offers to release Eric and Brian's friends if Brian agrees to convert, but Brian refuses. The bright lights are destroyed and they are all placed with Maurice in a locked dungeon-type room. They manage to escape by turning Maurice into a pile of clothes via an improvised light and slide him through the door crack. They re-arm themselves with more powerful lights, recruit Ronnie, and venture back into the monster world. They return to Boy's domain, and are able to defeat him, while Maurice defeats Snik with a flamethrower.

Unfortunately, Brian and the others find that they cannot return home because the sun has risen. Faced with the prospect of turning into monsters if they do not return to the human world by sunrise, the children travel in the monster world from the Eastern time zone to Malibu where the sun has not risen yet and they manage to escape. Before entering the human world, Brian shares a heartfelt goodbye with Maurice, who gives Brian his leather vest as a memento, promising to meet again with him someday. The kids run to a payphone and Brian calls home to say that he and Eric are in Malibu and begins to explain their story to their parents.

Fred Savage ... Brian

Howie Mandel ... Maurice

Daniel Stern ... Glen Stevenson

Margaret Whitton ... Holly Stevenson

Rick Ducommun ... Snik

Frank Whaley ... Boy

Ben Savage ... Eric

William Murray Weiss ... Todd

Devin Ratray ... Ronnie Coleman

Amber Barretto ... Kiersten

J. Michael Hunter ... Mr. Finn

Tom Hull ... Principal

Magbee ... Bus Driver

Lisa Cain ... Holly's Friend

Tony Bonsignore ... Beach Bum

Dana Wood ... Arnold

Byron Faler ... Schmoog

Doug Turner ... St. Louis Monster

Donna Strickland ... TV Guest

Howard Spiegel ... Father

Jessica Hauser ... Innocent Girl

Jessica Greenberg ... Painted Face Girl

Natanya Ross ... Kid on Trial

Michael Weaver ... Kid on Trial

Luke Greenberg ... Kid on Trial

Morgan Greenberg ... Kid on Trial

Alexander Kroll ... Kid on Trial

Herbert Duarte ... Kid on Trial

Kala Savage ... Little Monster

Rachel Ann Weiss ... Little Monster (as Rachel Weiss)

Matt Cavenaugh ... Little Monster

Amy Holden... Little Monster

Stacy Pochowicz ... Little Monster

Laura Winstead ... Little Monster

Elise Schillmoller... Little Monster

Trent Jobin ... Little Monster

Amy Plaskett ... Little Monster

Ashley Broadfoot ... Little Monster

Ginny Broadfoot ... Little Monster

Jeremy Fowler ... Little Monster

Scott Bayzle ... Little Monster

Matthew Norton... Little Monster

Davy Beard ... Little Monster

Brian's father Glen is played by Daniel Stern, who was working on The Wonder Years as the elder, retrospective (voice-over) version of Savage's character, Kevin Arnold. Real-life siblings Fred and Ben Savage play the respective roles of siblings Brian and Eric Stevenson, and their sister Kala plays a little monster