Ryan, Winnie the Pooh, Ash, Michelle and the rest of their friends meet two scientists, Dr. Elena Kinder (Kathleen Turner) and Dr. Heep (Christopher Lloyd), use genius-baby studies to fund BabyCo's theme park "Joyworld". According Dr. Kinder's Research, babies are supposed to possess vast, universal knowledge and speak a secret yet impossible-to-translate baby prelanguage called "Babytalk". At age two, however, the knowledge and language are lost as the babies "cross over" by learning how to talk. Most of the babies that were raised in Dr. Kinder's vast, underground research facility were adopted from the Pasadena orphanage, transformed into geniuses through use of the Kinder Method, and then used in experiments to decipher the language used by the baby-geniuses. One mischievous toddler, Sylvester (AKA Sly), makes repeated attempts to escape Dr. Kinder's research facility and one night, Sylvester goes into a dirty diaper truck and he actually succeeds. The next morning, one things Sylvester does not expect is to run into his twin, Whit, in a mall playground. Although Sylvester and Whit share a telepathic bond, they have no idea of each other's existence. While the guards from Dr. Kinder's research facility capture Whit, mistake him for Sylvester, and take him back to Dr. Kinder's research facility, Sylvester is taken home by Whit's adopted mother, Robin (Kim Cattrall), who is Dr. Kinder's niece. After Dr. Kinder is horrified that Whit and Sylvester switched at the mall, she decides to do a cross evaluation on Sylvester and Whit. However, when she comes to Dan Bobbin's place, she realizes that Dan Bobbin can understand babies. After the attempts to retrieve Sylvester fail, Dr. Kinder decides to move the research facility to Lichtenstein, so that they can transform Whit into becoming a genius thanks to him getting bred by the Kinder Method (thus erasing his memories about his foster parents, foster brothers and foster sisters) and use him as an experiment to crack the code to "Babytalk". The babies at Bobbin's place hypnotize Lenny (Dom DeLuise), the bus driver to drive to Dr. Kinder's research facility. Once at the research facility, Sylvester goes to the control room to set the robots from the theme park on the lab scientists. When the Bobbins return home, their natural daughter Carrie tells her father that the children are in Dr. Kinder's research facility. At the end of the fight Dr. Kinder captures Whit and takes him to the helicopter pad on the roof. Robin and Dan chase them to the roof, where Dr. Kinder reveals that she and Robin are not related, and that Robin was adopted at age two. After Dr. Kinder got arrested by the police, Sylvester and Whit come together on the roof to cross over. Dan and Robin adopt Sylvester. Dan is still curious of the secrets of life, but as the twins have crossed over they no longer know those secrets. Ryan, Winnie the Pooh, Ash, Michelle, the rest of thier friends, Carrie, their sister, doesn't reveal anything (just gives her dad a sly smile) because adults aren't meant to know their secrets.
- Bobby, Cindy, Oliver, Matthew, Dwayne, Steve, DJ, Stephanie, Michelle, Malcolm, Resse, Dewey, Mallory, Renee, Daisy, Gabriella, Gerald, May, Sid, Kady, Franklin and The Gang, Alvin, Simon, Theodore, Brittany, Jeanette, Elanor, Ben Hilton, Jamie, Max, Becca, Nicky, Jeannie, The Flash/Tony, Crispin, Dylan, Duncan, Sean, Tony's Brother, German Speaking Boy, Juel, Erin, Benny, Lina, Henry, Kiki, Dennis The Menace & Friends, Pete & Pete, Richelle, Littlefoot, Cera, Ducky, Petrie, Spike, SpongeBob SquarePants, Patrick Star, Bloom, Stella, Flora, Musa, Tecna, Layla, Roxy, Simba, Timon, Pumbaa, Zazu, Terk, Tantor, Baloo, Bagheera, King Louie, the Vultures (Buzzie, Flaps, Ziggy, and Dizzy), Jiminy Cricket, Alex, Marty, Melman, Gloria, the Penguins of Madagascar (Skipper, Kolwalski, Rico, and Private), Genie, Louis, Roger Rabbit, Danny, Sawyer, Rex, Dweeb, Woog, Esla, Rapunzel, Pascal, Flynn Rider, Maximus, Jean-Bob, Speed, Puffin, Chanticleer, Wilbur the Albatross, Owen, Lindsay, Beth, Strawberry Shortcake and her friends, Danny Phantom, Sam Manson, Tucker Foley, Jazz Fenton, Danny, Sawyer, Jean-Bob, Speed, Buddy, Tiny, Puffin, Rex, Dweeb, Woog, Elsa, Rapunzel, Pascal, Flynn Rider, Maximus, Chanticleer, Wilbur the Albatross, Bob the Tomato, Larry the Cucumber, Junior Asparagus, Hercules, Megara, Philoctetes, Pegasus, Alice, Pocahontas, Meeko, Flit, Princess Aurora, Prince Phillip, Peter Pan, Tinkerbell, Rosetta, Silvermist, Idressa, Fawn, Oliver, Dodger, Lucky, Cadpig, Rolly, Spot the Chicken, Woody, Buzz Lightyear, Jessie, Tommy Pickles, Chuckie Finster, Simon, Theodore, Brittany, Huckle, Lowly, Woody Woodpecker, Ord, Cassie, Arthur Read Ash and his friends, Ronald McDonald and his friends, Bob the Tomato, Larry the Cucumber, Junior Asparagus, Laura Carrot, Jimmy and Jerry Gourd, Mr. Nezzer, Mr. Lunt, the Powerpuff Girls (Blossom, Bubbles, and Buttercup), Professor Utonium, Miss Keane, Blue the Puppy, Ploka Dots, Slippery Soap, Tickety Tock, Mr. Salt, Mrs. Pepper, Paprika, Periwinkle, Roar E. Saurus, Fredrica the Birthday Girl, Zazu, Rafiki, Kovu, Kiara, Terk, Tantor, the All-Grown Up Gang, Grandpa Lou Pickles, Carly Shay, Sam Puckett, Freddie Benson, Spencer Shay, Gibby, The Gummi Bears, 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, 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), Popeye, Olive Oyl, Popeye's Nephews (Peepeye, Poopeye, Pipeye, and Pupeye), Wimpy, 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, Team Chaotix (Vector the Crocodile, Espio the Chameleon, and Charmy the Bee), Silver the Hedgehog, Blaze the Cat, Spyro the Dragon, Sparx the Dragonfly, Banjo and Kazooie, The Griffins (Peter, Lois, Chris, Meg, Brian, and Stewie), Glenn Quagmire, Cleveland Brown, The Teenage Mutant Ninja Turtles, Harry Potter, Hermoine Granger, Ron Weasley, Anastasia, Alex, Marty, Melman, Gloria, the Penguins of Madagascar (Skipper, Kowalski, Rico, and Private), King Julien, Maurice, Mort, Vitaly, Gia, Stefano, Marlene, Baloo, Bagheera, King Louie, Kit Cloudkicker, Rebecca Cunningham, the Vultures, Pinocchio, Jiminy Cricket, Geppetto, Woody, Buzz Lightyear, Jessie, Hamm, Slinky Dog, Rex, Mr. Potato Head, Mrs. Potato Head, the Squeeze Toy Aliens, Bullseye, Dolly, Mr. Pricklepants, Buttercup, Trixie, Chuckles the Clown, the Incredibles (Bob, Helen, Dash, Violet, Jack-Jack, and Frozone), Cinderella, Snow White, Ariel, Sebastian, Belle, Lumiere, Cogsworth, Mrs. Potts, Chip the Cup, Aladdin, Princess Jasmine, Genie, Abu, Mulan, Mushu, Cri-Kee, Pocahontas, Meeko, Flit, Princess Aurora, Princess Tiana, Louis, Rapunzel, Flynn Rider, Pascal, Maximus, Princess Merida, Peter Pan, Tinker Bell, Terence, Fawn, Rosetta, Silvermist, Iridessa, Vidia, Lucky, Cadpig, Rolly, Spot the Chicken, Alice, Hercules, Megara, Phlioctetes, Pegasus, Phineas and Ferb, Candace Flynn, Isabella Garcia-Shapiro, Stacy Hirano, Buford, Baljeet, Perry the Platypus, Kids World's Adventures Team, and the characters will guest star in this film.