Maggie squeaks her toy, which causes a chain reaction of anger in the family--Lisa attacks Maggie for making noise, Bart attacks Lisa for shoving a baby, Homer attacks Bart for hitting a girl, and Grampa attacks Homer for hitting a kid.
Bart tries to hide one of the cookies he stole from the jar by distracting his parents with the shell game. Although his plan seems to succeed, he is busted by Maggie, who then eats the cookie.
The kids are watching TV and Homer tells them to stop watching "The Itchy and Scratchy Show" because it's "too violent." Unable to watch cartoons, Bart puts on his own show.
Marge and Homer throw the kids into their toy room and tell them to "play nice." A frustrated Bart takes out his anger on a punching bag; Lisa then takes a turn and adds motivation by drawing Homer's face on the bag.
The kids get to see Krusty the Clown's show live for the first time. Bart believes Krusty is an impostor and exposes it on television, much to his parents' dismay.
When Bart is sent outside to exercise his legs by Homer's orders, he gets handsomely rewarded for stopping a burglar from robbing a candy store. But he asks for the reward to be in candy bars, much to Homer's dismay.
After the kids are ordered to clean their room by Homer and Marge, Bart forces his sisters to do all the work while he tells a story about a parallel world where large kids are the bosses of their small parents, who are made to do chores.
Bart, Lisa and Maggie go to the movies to see "The Return of the Happy Little Elves", but Bart convinces the girls to see "Revenge of the Space Mutants" instead.
When Homer sees Bart, Lisa and Maggie going crazy and bouncing off the walls, he and Marge try using hypnotism to tame the kids. They pretend to become mindless zombies.
Bart, hungry for chocolate bars, steals some from the supermarket. He is quickly caught by security, but when the guard leaves the room to talk to his boss, he sneakily eats the candy and claims the cops have "no evidence."
The family discovers that someone has eaten every last cookie in the cookie jar. The culprit turns out to be Bart, who later has a terrible nightmare in which he is only an inch tall and nearly crushed by giant cookies in the kitchen.
Homer takes the family to a psychologist. The Simpsons drive the psychologist over the edge and learn that this was just the cure that the family needed.
After Maggie accidentally kicks her ball on Bart's face, he kicks it out of sight and she takes off to retrieve it. She ends up being caught on a branch.
While Homer is watching his TV show, Bart flies a kite outside with Maggie and Lisa. The wind suddenly blows and the kite gets stuck on the TV antenna, which messes up the reception.