Big (1988)

Josh Baskin would do anything to be big to hang out with his crush, Cynthia, at the carnival. He finds a Zoltar machine, and he wishes to be big. After Zoltar tells him, "Your wish is granted," he notices that it's unplugged. He wakes up the next morning in an adult's body, but he still has the same personality. With the help of his best friend, Billy, he learns how to act like an adult. But as he gets a girlfriend and a fun job, he doesn't want to be a kid again. Will Josh stay big or become a 13-year-old boy again?