After years of pursuing drug dealer Cullen Crisp (Richard Tyson), Los Angeles Police Detective John Kimble (Arnold Schwarzenegger) has him on a murder charge after Crisp shot and killed an informant who had given him information regarding the whereabouts of his ex-wife, Rachel Myatt Crisp, and his son Cullen Jr. However, the only witness, a drug-addicted girl named Cindy, the informant's girlfriend who was hiding at the time of the murder, is deemed too unreliable to put Crisp up for a permanent prison charge as she changes her mind about testifying, so Rachel Myatt has to be found and persuaded to testify.Kimble, accompanied by Detective Phoebe O'Hara (Pamela Reed), a former teacher, goes undercover in Astoria, Oregon, to find Crisp's ex-wife Rachel. It is believed that Rachel stole millions of dollars from Crisp before fleeing. The detectives plan to offer her a deal to testify against Cullen in exchange for immunity. O'Hara is to act as the substitute teacher in the son's kindergarten class at Astoria Elementary School, while Kimble is to discover the identity of the mother.Unfortunately, O'Hara, who is hypoglycemic, falls ill with a terrible case of stomach flu at the last moment, so Kimble takes the teacher's job. The school principal, Miss Schlowski (Linda Hunt), is suspicious, but Kimble adapts progressively to his new status even though he has no formal teaching experience. Using his pet ferret as a class mascot, his police training as a model for structure of the classes, and positive reinforcement, he becomes a much-admired and cherished figure to the children. In turn, Kimble begins to love his cover job and his young charges, to the point where he personally deals with a case of child abuse. He first speaks to the cowardly mother and tells her to warn her husband that he will press charges if he abuses their child again, and when the father takes no notice, Kimble assaults him in front of some students, finally winning Miss Schlowski's favor.One of Kimble's students is a boy named Dominic. Kimble becomes fond of Dominic's mother, Joyce Palmieri (Penelope Ann Miller), who also works at the school. Joyce, like many other of the students' mothers, is estranged from her husband, so much that she will not speak of him. This raises Kimble's suspicions. In a series of conversations with the gradually more trusting Joyce, Kimble deduces that she has to be Rachel Myatt and that Dominic is Crisp's son. O'Hara, who has been posing as Kimble's sister, agrees with his deductions.Meanwhile, back in California, Cindy dies after using spiked cocaine provided by Crisp's mother, Eleanor Crisp (Carroll Baker). The case against Crisp is dismissed because the prosecution has no other evidence. Crisp is freed from prison and he and his mother immediately head to Astoria, where they begin looking for the child using the information from the informant. Breaking their cover, Kimble and O'Hara admit to Joyce who they are and that they know who she really is. They offer her immunity for her testimony about where she hid Crisp's money. Joyce reveals that she never stole any of his money; it was a lie he told to incite the underworld to find her and Dominic for him.As Joyce frantically prepares to go on the run again, Dominic runs away and Kimble and Joyce find him climbing up a microwave tower to retrieve something he had placed there to alert him if "the bad people" were coming. Dominic's backpack gets caught on the ladder and Kimble climbs up to rescue him. Later, Kimble admits to Joyce the truth about his family; he has a 13 year old son he hasn't seen in years, his ex-wife remarried and told him she doesn't want him involved in his son's life. He then promises Joyce she and Dominic will never have to run again.The next day, while O'Hara gives Kimble's class a safety lesson about strangers, Crisp starts a fire in the library at the school in order to grab his son in the chaos, but he is seen. Crisp takes Dominic hostage when Kimble confronts him, but Crisp is bitten by the ferret (which Dominic had rescued at the sound of the fire alarm) and Dominic wriggles free. Crisp shoots Kimble in the knee but Kimble shoots and kills Crisp before he can hurt Dominic. Meanwhile, noticing that O'Hara is trying to help Kimble apprehend her son, Eleanor knocks over O'Hara with her rental car. She ventures into the school, finds Kimble, and shoots him in the shoulder, but then discovers her dead son's body. Before she can shoot Kimble again and kill him, O'Hara arrives on the scene and knocks her unconscious with a baseball bat.Crisp's mother is arrested, while the unconscious Kimble (much to the sadness of the children) is hospitalized. During Kimble's recovery, O'Hara and her fiancé Henry come to visit him in the hospital. Henry, a chef, brings in Kimble some "better" food (as O'Hara claimed to Kimble's nurse that he shouldn't be eating jello because he is a tough guy). After Henry accidentally pulls on his broken leg, they invite him to their wedding. Kimble tells them that he'd love to come, and O'Hara asks him where they should send the invitation.After Kimble recovers, he decides to retire from the police force and returns to teaching at the school. Miss Schlowski hands him his police whistle, and, with a smile, tells him that the kids are his. The kids (after Kimble blows his whistle) are very happy to see him (especially Dominic), and Kimble announces that he is back. Joyce, who is talking about the civil war, hears the happy shouts coming from the class, and asks her class to excuse her. She comes into the classroom and sees Kimble, who turns around to see her. Joyce smiles at him, while a friend of Dominic's says that they are going to "do it". Joyce runs up to Kimble (who is very happy to see Joyce) and she kisses him in front of all of the kids, who shriek with joy at his return, and at his new relationship.
- DJ, Malcolm, Greg, Marcia, Peter, Jan, Malcolm, Mallory, Resse, Renee, Dewey, Daisy, Mother Goose Club Gang, Alvin, Brittany, Simon, Jeanette, Theodore, Eleanor, All That Gang, Bindi, Rosie, CeCe and her friends, Sharkboy, Lavagirl, Max, Linus, Marissa, Aldo, Ethan, Marissa, Bina, Ely, Otter, Ramona, Earl and his family, Bob the Tomato, Larry the Cucumber, Junior Asparagus, Laura Carrot, Jimmy and Jerry Gourd, Mr. Nezzer, Mr. Lunt, Jean-Claude and Phillipe, Peter Pan, Tinker Bell, Fawn, Rosetta, Silvermist, Iridessa, Terence, Vidia, Periwinkle, Lucky, Cadpig, Rolly, Spot, Alice, Hercules, Meg, Phil, Pegasus, Pocahontas, Meeko, Flit, Princess Aurora, Woody, Buzz Lightyear, Bo Peep, Jessie, Rex, Hamm, Slinky Dog, Mr. Potato Head, Mrs. Potato Head, the Squeeze Toy Aliens, Bullseye, Dolly, Mr. Pricklepants, Buttercup, Trixie, Chuckles the Clown, The Teenage Mutant Ninja Turtles, The Smurfs (Papa Smurf, Smurfette, Gutsy Smurf, Brainy Smurf, Clumsy Smurf, and Grouchy Smurf), Oscar the Sharkslayer, Lenny the Shark, Angie, Don Lino, Mr. Sykes, Ernie and Bernie, Luca, Boog and Elliot, Wolf and Twitchy, Rodney Copperbottom, Bigweld, Fender Pinwheeler, Piper Pinwheeler, Lug, Diesel Springer, Crank Casey, Aunt Fanny, Dexter, DeeDee, Cow and Chicken, I.M. Weasel and I.R. Baboon, Bloo, Mac Foster, Frankie Foster, Eduardo, Coco, Wilt, The Powerpuff Girls (Blossom, Bubbles, and Buttercup), Blue the Puppy, Ploka Dots, Slippery Soap, Tickety Tock, Mr. Salt, Mrs. Pepper, Paprika, Periwinkle, Roar E. Saurus, Fredrica the Birthday Girl, Rafiki, Kovu, Kiara, the All-Grown Up Gang and their families, Carly Shay, Sam Puckett, Freddie Benson, Spencer Shay, Gibby, Tori Vega, Andre Harris, Robbie Shaprio, Cat Valentine, Beck Oliver, Trina Vega, Rex Powers (puppet), Popeye, Olive Oyl, Popeye's Nephews (Peepeye, Poopeye, Pipeye, and Pupeye), Wimpy, Ludwig von Drake, Scrooge McDuck, Huey, Dewey, Louie, Webby, Launchpad McQuack, Darkwing Duck, Gosalyn /Mallard, Honker Muddlefoot, Chip and Dale, Gadget Hackwrench, Monterey Jack, Zipper, Lilo, Stitch, Pleakey, Jumba, Nani, the Muppets (Kermit the Frog, Miss Piggy, Fozzie Bear, Gonzo, Bean Bunny, Rowlf the Dog, Scooter, Rizzo the Rat, Waldorf and Statler, Pepe the King Prawn, Sweetums, Thog, Sam the Eagle, the Electric Mayhem and Walter), The Simpsons (Homer, Marge, Bart, Lisa, and Maggie), Ned Flanders, Rod and Todd Flanders, Milhouse Van Houten, Krusty the Clown, Moe Szyslak, Barney Gumble, Ronald McDonald, Grimace, Hamburglar, Birdie, Sundae, Mario, Luigi, Princess Toadstool, Toad, Yoshi, Donkey Kong, Diddy Kong, Sonic the Hedgehog, Miles "Tails" Prower, Knuckles the Echidna, Amy Rose, Cream the Rabbit, Cheese the Chao, Shadow the Hedgehog, Rouge the Bat, E-123 Omega, Team Chaotix (Vector the Crocodile, Espio the Chameleon, and Charmy the Bee), Silver the Hedgehog, Blaze the Cat, Pac-Man, Cylindria, Spiral, Sir Cumference, The Ghost Gang (Blinky, Inky, Pinky, and Clyde), Spyro the Dragon, Sparx the Dragonfly, Banjo and Kazooie, Princeton, Kate Monster, Rod and Nicky, Trekkie Monster, Barney the Dinosaur, Baby Bop, BJ, Riff, Lightning McQueen, Mater, Sally Cerera, Luigi and Guido, Gru, Agnes, Edith, Margo, the Minions, Wreck-It Ralph, Vanellope Von Schweetz, Fix-It Felix Jr., Sargeant Calhoun, The Griffins (Peter, Lois, Chris, Meg, Brian, and Stewie), Glenn Quagmire, Cleveland Brown and his family, Joe Swanson, Blu, Jewel, Rafael, Luiz, Yakko Warner, Wakko Warner, Dot Warner, B1 and B2, The Teddies (Morgan, Amy, and Lulu), Rat-in-a-Hat, Clifford the Big Red Dog, Cleo, T-Bone, Mac, Emily Elizabeth, Jetta Handover, Charley, Arthur Read, D.W. Read, Muffy, Francine, Buster, Binky Barnes, Alan 'Brain' Powers, Fern, Sue Ellen, Prunella, Sid, Diego, Manny, Ellie, Peaches, Crash and Eddie, Harry Potter, Hermoine Granger, Ron Weasley, Hagrid, Courage the Cowardly Dog, Johnny Bravo, Ami and Yumi, Sulley and Mike, Celia Mae, the Incredibles (Bob, Helen, Dash, Violet, Jack-Jack, and Frozone), Cinderella, Snow White, The Seven Dwarfs, Belle, Lumiere, Cogsworth, Mrs. Potts, Chip the Cup, Rapunzel, Flynn Rider, Pascal, Maximus, Princess Merida, Princess Anna, Elsa, Olaf, Kristoff, Sven, the Recess Gang (TJ, Vince, Mikey, Ashley, Gretchen, and Gus), Phineas and Ferb, Candace Flynn, Isabella Garcia-Shapiro, Stacy Hirano, Buford, Baljeet, Perry the Platypus, Stan Marsh, Kyle Broflovski, Eric Cartman, Kenny McCormick, Butters Stotch, Ike Broflovski, Wendy Testaburger, Big Bird, Oscar the Grouch, Snufffy, Elmo, Zoe, Prairie Dawn, Grover, Bert and Ernie, Cookie Monster, Telly Monster, Baby Bear, Rosita, Count von Count, Abby Cadabby, Fievel Mousekewitz, Tiger, Tony Toponi, Tanya Mousekewitz, Yasha Mousekewitz, Papa Mousekewitz, Mama Mousekewitz, Rafiki, Garfield, Odie, Jon Arbuckle, The Gummi Bears, Finn and Jake, Chloe King, Alek Petrov, Paul, Brian Rezza, Jasmine (The Nine Lives of Chloe King), Amy, Jake the Pirate, Izzy, Cubby, Skully, Bear, Ojo, Pip and Pop, Treelo, Peanut Otter, Butter Otter, Jelly Otter, Flick Duck, Pinch Raccoon, Scootch Raccoon, Ootsie and Bootsie Snootie, Olie Polie, Zoey Polie, Spot (Rolie Polie Olie), Percy and Bromley Polie, Ash Ketchum, Pikachu, Misty, Togepi, Brock, Littlefoot, Cera, Ducky, Petrie, Spike, Chomper, Ruby, Guido, Grandpa Longneck, Grandma Longneck, Billy Bevel, the rest of the characters, the Bowser family, and lots of villains will guest star in this film.