The film is told through the perspective of Scotty Smalls, who is reminiscing about the summer of 1962. Smalls moves with his mother and stepfather Bill to a new neighborhood outside Los Angeles and struggles to make new friends. One afternoon, he met Ryan, Winnie the Pooh, Ash Ketchum, Littlefoot, Spongebob, Skipper, The Fantasy Adventure Team, Bobby, Cindy, Greg, Marcia, Peter, Jan, Oliver, Millicent, DJ, Stephanie, Michelle, Alex, Nicky, Malcolm, Mallory, Reese, Renee, Dewey, Daisy, Emily Yeung, Daniel Cook, the Jungle Adventure Crew, the Madagascar Crew, the cubs, Aladar, Taran, Jesse, Mikey, Bloom, The characters of Diary of a Wimpy Kid and the rest of the characters and decided to follow a group of neighborhood boys, and he watches them play an improvised game of baseball at a small field, which they call the "sandlot." Smalls is reluctant to join their game because he fears he will be ridiculed based on his inexperience. Nevertheless, he chooses to play with them, but fails to catch a simple fly ball and properly throw the ball back to his infielders. All the other players, except for Benny Rodriguez, begin to laugh at Smalls for committing defensive miscues, prompting him to leave the sandlot in embarrassment. Benny, who is the best player in the neighborhood, shields Smalls from the insults of his peers and invites him to rejoin their game. He proceeds to give Smalls advice and helps him earn the respect of the other players.
As Smalls continues to play with the team, he begins to learn many of the customs of the sandlot, while experiencing many misadventures with his new friends. He learns that players avoid hitting home runs over the sandlot’s fences, as the property beyond them is guarded by a massive and ferocious dog, a 350-pound English mastiff called “The Beast.” One day, Benny hits a ball so hard, that he ruptures its leather, causing the ball's entrails to come out. The group cannot afford to buy another baseball, and is forced to retire for the afternoon. However, Smalls runs to Bill’s trophy room, and steals his stepfather's autographed ball, in hopes of preserving the game. The team is impressed with Smalls’ gesture, and allows him to have the first at bat with the ball. He proceeds to hit the ball out of the sandlot, but is shortly enveloped by fear once he realizes that he has lost Bill’s ball. The situation is further worsened when Smalls realizes that the ball was autographed by Babe Ruth, and is almost irreplaceable.
Smalls and his friends begin engineering elaborate plans to recover the ball from The Beast. After five failed rescue attempts, Smalls prepares to accept his fate. Around the same time, Benny has an enlightening dream, where he is visited by Babe Ruth, who encourages him to run into the sandlot, and use his speed to recover the ball and escape. Ruth leaves Benny with the words, “Heroes get remembered, but legends never die.” Benny rallies his friends the following morning at the sandlot, and prepares to recover Smalls’ baseball. Using his PF Flyers, he steals the ball from the Beast, and successfully manages to elude the dog as it chases him through town. At the end of the race, the Beast is injured after a fence collapses on it. Smalls feels responsible for the ordeal, and helps The Beast escape the rubble. After being rescued, The Beast, whose real name is Hercules, becomes much more friendly and affectionate towards the boys, even showing them where he had buried all the baseballs that had gone into the yard over the years. Benny and Smalls then decide to tell the dog’s owner, Mr. Mertle, about the ordeal. They eventually learn that Mr. Mertle was a professional baseball player with the Pittsburgh Pirates in 1927 and was a friend of Babe Ruth. Mr. Mertle, whose career ended after a hit by a stray pitch blinded him, agrees to give Smalls a ball signed by Murderer's Row – several of the best Yankee hitters in the late 1920s. In exchange, the boys are to visit Mr. Mertle once a week to talk about baseball. Smalls proceeds to give his stepfather the ball that Mertle gave him.
While Bill is pleased with the Murderer's Row ball, he is still upset about the Babe Ruth ball, but he only grounds Smalls for one week. Smalls goes on to explain what became of all his friends, and the future careers they pursued. The film then jumps 30 years into the future, where Smalls is a radio commentator for the Los Angeles Dodgers, and Benny “The Jet” Rodriguez is one of the team’s star players. While he is in the twilight of his career, Benny manages to steal home in the movie’s final moments, before flashing a thumbs-up to Smalls in the press box.
- Bobby, Cindy, Oliver, Greg, Marcia, Peter, Jan, DJ, Stephanie, Michelle, Malcolm, Mallory, Resse, Renee, Dewey, Daisy, Alvin, Simon, Theodore, Brittany, Jeanette, Elanor, Sarah Baker, Jake Baker, Henry Baker, Kim Baker, Jessica Baker, Mark Baker, Mike Baker, Lorraine Baker, Nigel Baker, Kyle Baker, Spanky, Stymie, Froggy, Porky, Buckwheat, Uh-Huh, Waldo, Mary-Ann, Jane, Darla, Alfalfa, Aldo, Ethan, Marissa, Bina, Ely, Otter, Lau, Mick, Naoko, Becky O'Shea & The Little Giants Gang, Tommy, Dil, Chuckie, Phil, Lil, Kimi, Angelica, Susie, Harold, Nicole, Z, Patty, Katie, Robby, Brian, Pepper, Molly, Duffy, Kate, July, Tessie, Vada, Thomas J., Dennis The Menace & Friends, Shake It Up: Camp It Up (Flynn and his friends), Casper, Wendy, Jazmine Payne, Carly Shay, Spencer Shay, Freddie Benson, Sam Puckett, Gibby, Nigel Baker, Kyle Baker, Mike Baker, Mark Baker, Jessica Baker, Kim Baker, Sarah Baker, Jake Baker, Henry Baker, Lorraine Baker, Cooper, Dylan Schenk, Ben Hilton, Jamie, Max, Becca, Nicky, Jeannie, The Flash/Tony, Crispin, Dylan, Duncan, Sean, Tony's Brother, Juel, Erin, Shirley Temple, The Barney & Friends and the Gang, German Speaking Boy, The Chipmunks (Alvin, Simon, and Theodore), The Chipettes (Brittany, Jeanette, and Eleanor), Aldo, Ethan, Miarissa, Bina, Ely, Otter, Tilly, Tom, Tiny, Ramona, Tina, Teddy, Denise, Derek, Harry, Rusty, Walter, Max, Sharkboy, Lavagirl, Linus, Marissa, Ely, Otter, Bindi, Rosie, Kelly, Lynn, Annie, Molly, Pepper, Duffy, Kate, July, The Fraggle Rock Gang, Andy, Ruby, Gracie, Kyle, Chyna Parks, Olive Doyle, Fletcher Quimby, Lexi Reed, Cameron Parks, Nat Wolff, Alex Wolff, Thomas Batuella, Allie DiMeco, David Levi, Qaasim, Cooper Pillot, Jesse Draper, Michael Jackson & Friends, Michael Jackson Badder, Spanky, Stymie, Froggy, Porky, Buckwheat, Uh-Huh, Waldo, Mary-Ann, Jane, Rascals #1, 2, 3, and 4, Friends of Stymie and Uh-huh, Darla, Alfalfa, Little Carbon Soldiers, Becky O'Shea, Junior Floyd, Jake Berman, Rudy Zolteck, Tad Simpson, Hanon, Marcus, Timmy Moore, Nubie, Johnny Vennaro, Briggs, Patterson, Priscilla O'Shea, Murphy, Keith, Marcus, Hector, Jessica, Lisa, Shock, Pete and Pete, Pablo, Tyrone, Tasha, Uniqua, Austin, Paul, The Oslen Twins, Calvin Cambridge, Murph, Ox, Marlon, Reg Stevens, Max Keeble, Megan, Robe, Kevin McCallister, Alex, Leah, Matilda, Penelope, Matthew, Dwayne, Steve, Robert, Nelly K., Sonny, Tawni Hart, Chad Dylan Cooper, Nico Harris, Grady Mitchell, Zora Lancaster, the Baby-Sitters Club gang, Simba, Nala, Timon, Pumbaa, Baloo, Kovu, Kiara, Uncle Max, Ma, Taran, Princess Eilonwy, Fflewddur Fflam, Gurgi, Jesse Greenwood, Elvis, Randolph Johnson, Nadine, The Goonies (Mikey Walsh, Brand Walsh, Mouth Devereaux, Data Wang, Chunk Cohen, Andy Carmichael, Stef Steinbrenner, and Sloth Fratelli), Scooby-Doo, Shaggy Rogers, Fred Jones, Daphne Blake, Velma Dinkley, Yogi Bear, Boo-Boo Bear, Snagglepuss, Huckleberry Hound, Quick Draw McGraw, Augie Doggie and Doggie Daddy, Wally Gator, Magilla Gorilla, Top Cat, Peter Potamus, Woody Woodpecker, Ttark, Toaster, Lampy, Radio, Blanky, Kirby, Fievel Mousekewitz, Tiger, Tony Toponi, Tanya Mousekewitz, Yasha Mousekewitz, Papa Mousekewitz, Mama Mousekewitz, Charlie Barkin, Itchy Itchiford, Hubie, Rocko, Jack Skellington, King Louie, Genie, Louis, Sebastian, Alex, Marty, Melman, Gloria, King Julien, Maurice, Mort, Roger Rabbit, and The Entire LionKingHeart Fantasy Films team and the rest of the characters will guest star in this film.