After leaving the prison, the dwarf criminal Calvin Sims joins to his moron brother Percy to steal an expensive huge diamond in a jewelry for the mobster Walken. They are chased by the police, and Calvin hides the stone in the purse of the executive Vanessa Edwards, whose husband Darryl Edwards wants to have a baby. Percy convinces Calvin to dress like a baby and be left in front of the Edwards's house to get inside the house and retrieve the diamond. Darryl and Vanessa keep Calvin for the weekend and decide to adopt him, while Walken threatens Darryl to get the stone back.
A short and tiny criminal named Calvin has just committed a robbery involving stealing a precious diamond from a jewelry store along with his dim-witted partner, Percy. However, the snatch goes awry, and Calvin ends up ditching the diamond by stashing it in a woman named Vanessa's purse. Vanessa happens to be married to a wannabe-dad named Darryl. Calvin must now pose as a young infant in order to retrieve the stolen diamond. However, a simple quick-and-grab turns into a friendly relationship between Calvin and Darryl.
A wannabe dad mistakes a vertically challenged criminal on the lam as his newly adopted son.
- Calvin (Marlon Wayans) has just been released from prison. They open the door of the prison to reveal him to be a midget. His accomplice, wannabe rapper Percy (Tracy Morgan), picks up Calvin and tells him they need to get a diamond from a local jewelry store, which will pay each of them 50,000 dollars. Percy (P-Unit) says he needs it to start his record studio.
Meanwhile, at a swank restaurant, Darryl (Shawn Wayans) is talking to his friend Jimmy (David Alan Grier), telling him to come out when the time is right. Soon Vanessa (Kerry Washington) arrives and tells Darryl she has news. Right before she says it all, Darryl's friend pops out playing "Gonna Have My Baby". She says that she actually got a promotion, and he pops out singing "Celebration" before shouting out, "REMIX!" Eventually he is shooed by Darryl, and it is revealed she doesn't want a baby like Darryl does.
Eventually, Calvin and Percy reach the jewelry store, where the diamond is located. They go inside the store, with Calvin in a duffel bag. Percy puts down the bag and begins to talk to a worker, who, after Percy tells her he is a rapper, begins acting "gangsta" to get his business. Meanwhile, Calvin goes under the table holding the diamond and removes the diamond by sawing a circle under the table and removing it. Calvin then gets back in the bag and crawls back to where Percy dropped him. Also, a dog gets in the bag with Calvin not knowing. When Percy picks up the bag, an old lady notices her dog is missing and alerts security, leading to the diamond's disappearance being noticed. Percy runs out with the bag and they get in the car.
As they take off, they only drive around in circles, as a boot got put on their car. They then get out and run on foot as two police men chase them. They hide in a store while police find another black guy and begin beating him. Meanwhile, Calvin hides the diamond in a lady's purse to get rid of the evidence. Calvin and Percy meet up after police leave, believing they lost their man. They decide to follow the couple home.
When they reach their home, they discover that Darryl wants a baby. This leads to the idea to disguise Calvin as a baby and get the diamond back. Percy rings the bell and hides in the bushes. Darryl and Vanessa answer the door, finding the "baby" and a note from Percy asking them to take care for his baby because he could not. After an attempt to call child services, they discover they can't bring him in, as they're closed. When they change his diaper, they are in shock. Vanessa's father (John Witherspoon) lives with them. He's the only one who doesn't trust the baby. After Calvin coughs horribly, they decide to take him to the doctors.
At the doctors, they discover a scar from a knife fight or appendix removal, as well as a tattoo, which they blame on bad parenting. After the checkup, Calvin steals the purse with the diamond in it while Darryl and Vanessa try to figure out what they have to do with the baby. Darryl wants to keep him while Vanessa wants to get rid of him. Calvin, meanwhile, runs into a police officer outside the room, who treats him like a baby. Before he can check the purse, Vanessa finds him and grabs the purse. Right when she is about to turn Calvin over, he calls her "Mama", leading to her keeping him for the weekend. After bringing him home, they decide to invite their friends to meet the baby and loan them baby stuff for the weekend. During the weekend, Calvin has to suffer several unpleasant humiliations, such as bath time. He believes Vanessa will be joining him in the bath, only for it to be Darryl. Darryl strips naked, jumps in the bath and Vanessa leaves them. It is here that Darryl decides to relieve himself of a large build up of flatulence and breaks wind several times in the bath. Calvin is forced to suffer all through bath time, as Darryl's flatulence is incessant and he breaks wind powerfully and without hesitation.
Cut to Percy going into a shady bar run by mafia kingpin Walken (Chazz Palminteri) who offered to pay them for the diamond. He threatens Percy, telling him he had 24 hours before his goons would get involved.
Back at the home, Darryl and Vanessa's friends arrive. They include Greg (Lochlyn Munro), Brittany (Brittany Daniel), Richard (Fred Stoller) and Janet (Alex Borstein). They take turns trying to describe the ugly baby, such as "National Geographic Beauty". Brittany and Janet go into the kitchen with Calvin. Calvin pulls himself onto Brittany, who suggests breast feeding after he tugs at her breasts a few times. He says yes, expecting her to do it, but is sadly mistaken when Janet offers to do it. Calvin bites her and runs away. Soon we see their friends leave, with Brittany stopping to give Calvin a kiss, leading to him frenching her. After all their friends leave, Vanessa and Darryl put Calvin to bed.
Calvin decides to stay up and wait to take the diamond and leave, but is incapable of fighting off the lullaby, and falls asleep. He wakes up later that night and goes downstairs to call Percy and get the diamond. While on the phone, though, Pops comes in, shotgun in hand. He starts threatening Calvin before Darryl comes in. Darryl takes Calvin away, not believing Pops, and warms up some milk for him. He then sits Calvin down and begins an emotional speech about wanting to be a father. Vanessa watches as he talks, and finally laughs as Darryl and Calvin drink their milk. When asked why, she reveals the milk to be Janet's breast milk. This causes both of them to spit it out. Darryl and Vanessa begin getting romantic as Calvin watches in his crib. The next morning, Vanessa wakes up as Darryl comes in. She looks happy, saying she can't remember the last time they did it twice in one night. He looks puzzled as Calvin comes up from under the blanket.
Vanessa makes a nice breakfast for Pops and Darryl. Pops comes down while Calvin is watching a kids show. She gives Pops his breakfast while he turns the TV to the news. Right before they show a photo of Calvin, the suspect of the diamond heist, he repeatedly cries out D-Rex, leading Vanessa to change it back. Pops begins to read the paper as Calvin eyes his breakfast. Soon he jumps over and grabs his food, one item at a time. Eventually Pops realizes his food is gone and blames Calvin. Vanessa brushes him off as he leaves for a diner. Darryl comes down stairs and grabs his breakfast as Vanessa leaves for work. He begins to feed Calvin who hides his face, prompting a game of peek-a-boo. Soon Calvin gets tired of it and smacks him over the head with a frying pan. As Calvin drags Darryl's body, he grabs the diamond out of her purse. Vanessa comes back in as she forgot her purse and wakes up Darryl from his unconsciousness. She scolds him for sleeping, and he looks puzzled. Calvin hides the diamond in a diaper bag while Vanessa leaves.
Darryl and Calvin go to the park and play multiple games, each one resulting with Darryl getting hit between the legs. Eventually Darryl and his friends go for ice cream, leaving Calvin with Brittany and Janet. Percy shows up as Calvin tries to find the right diaper bag. He grabs one as the moms find him, thinking he was trying to kidnap Calvin. They chase Percy down as he tries to run off with the bag. He gets beaten before getting away. Darryl arrives and hears the news, deciding to take Calvin home. As they load the car, Calvin begs for keys. He keeps on whining and kicking Darryl in the shin until he gives Calvin the keys. Calvin gets in the car and takes off, leading Darryl to believe someone stole the car. He stops the mini van driver (Molly Shannon) and begs her to chase down the car. She does and drives like a mad man as she tracks down the car. After a lengthy chase, the car is stopped, and the police open the car to reveal Calvin crying in the backseat. The police are convinced the car jacker got away.
Calvin is tied up and Darryl debates going to a hockey game. They decide to go to the game with Calvin. At the game, Calvin takes the diamond and swallows it to hide it from Darryl. He then grabs a beer from the man next to him and drinks it to keep it down. The drink lady comes down and asks if he wants some more, and he gets some, as do Darryl and his two friends. Calvin makes a crude comment ("nice ass!") as the lady passes Darryl and she believes it was him, calling him a pig. Calvin calls her a tramp, and she pours a beer on Darryl. Calvin drinks the beer again, leading him(the guy to Calvins left) to believe Darryl did it. Soon a cheap check costs a visiting team's player a trip to the box as fans boo him. He then challenges all of them, and Calvin throws a beer at the man. The player, thinking it was Darryl, comes into the stands and Calvin climbs up on top of the player and attacks him. The man then throws Calvin to the ground and stomps on him. We see a bruised Calvin in bed as Darryl talks about not being a good father. Then he decides to throw Calvin a birthday party.
Percy brings the diaper bag to Walken, who opens it to reveal nothing but dirty diapers and other baby items. He is then told by the Walken that he'll give him more time, but he better deliver. After Percy leaves, the boss tells his men that he suspects betrayal by Percy's partner, and to follow Percy.
At the birthday party, Calvin picks a fight with D-Rex (Rob Schneider), by calling him a loser in a blue dinosaur suit who has no money. Then that leads to Calvin running behind D-Rex,ripping his tail wide open,crawling up into his suit, and beating him up from the inside! Eventually Darryl gets Calvin away from the dead D-Rex to play football with the other boys and their dads. At the start, the other team, led by Greg who stiff arms the children, are winning. Soon though, Calvin and another kid decide to kick it up a notch and use brutal force to take down the other team, leading them to victory. After Greg gets hit between the legs by Calvin making a touchdown, his son walks up to him(Greg),says "Dad,you suck!,"and kicks him in the head. Meanwhile, Darryl answers a knock at the door where Percy says he is Calvin's father here to get him. Darryl beats him up, which the mob goons see, leading them to believe Darryl was Percy's partner, and he took the diamond for himself.
Meanwhile, Pops watches the news at a diner and sees Calvin as the prime suspect in the diamond heist. He decides to stop him.
Back at the party, Calvin is given a cake and begins to cry, as he never had a birthday or parents. Pops shows up with a teddy bear, saying he was wrong about Calvin. Calvin goes inside where he sees Janet give her son Castor Oil. Calvin decides to drink it and poop out the diamond. He drinks it and goes as Vanessa and Darryl watch. Darryl leaves Vanessa to change his diaper, where she finds the diamond, thinking it to be a diamond for her ring, which had none. She decides to take him out to dinner, leaving Pops and Calvin alone. It is now that Calvin reveals to Pops that he is a criminal. He then beats up Pops and calls Percy, telling him to show up in an hour.
At the restaurant, Darryl tries to tell Vanessa that he didn't get that for her, but he stops when she says she wants to adopt Calvin. Afterwards, Vanessa and Darryl come home to find Pops strangling Calvin. Vanessa then calls the retirement home, who come to take away Pops. He shouts "The teddy bear knows!" Before being taken away. Vanessa puts Calvin in bed as she cries and goes in the bathroom. Darryl remembers the bear comment and finds the bear, revealing it to be a camera. He hooks it up to the TV, and watches as Calvin reveals himself not to be a baby to Pops on screen. He runs upstairs to tell Vanessa, both of whom discover Calvin to be missing as is the diamond.
Percy, while driving with Calvin, tells his partner that Walken thinks Darryl betrayed Percy and he has the diamond, so they are free to keep the diamond. Calvin realizes Darryl and Vanessa are in danger and he needs to go back. He does and finds Darryl, where the two confront each other about him lying about being a baby. Calvin apologizes, and before it can go any farther, the Walken and his two goons bust in. They threaten to hurt Calvin and Darryl. Eventually, Calvin knocks out the goons while the boss threatens Darryl while still maintaining his baby disguise. Calvin comes in and throws a plane that hits the boss below the waist. The police come in and arrest the mob boss and his goons. Calvin returns the diamond to the police and they tell Darryl he will receive a 100,000 dollar reward. After the police leave, Darryl and Calvin have a tearful goodbye, where Calvin reveals he liked being their kid. Darryl follows Calvin outside and they decide to go to a bar.
During the credits, though, Pops and Calvin are looking at Vanessa and Janet's baby. Calvin remarks that the baby looks just like his father.