Twelve year old Josh Baskin is on line to go on a ride at an amusement park. Directly behind him is a cute girl he knows from school, who strikes up a conversation with him. When he gets to the front, he is smaller than the wooden cutout used to determine whether one is big enough to go on the ride, and he is extremely humiliated. Moments later, he puts a coin in a fortune telling machine and is told to make a wish. In the wake of his embarrassment, he, innocently enough, wishes that he were big.
To his astonishment, when Josh awakes the next morning, his wish has been granted. Though still atwelve year old child in every respect but physically, his is longer recognizable to his mother, he must leave home and, once he learns that resolving his problem will take a long time, has no choice but to try to make his own way This means getting a job and mingling in the world of adults. As it turns out, the job he gets at a toy manufacturer is perfect for him, as his insight into what toys kids will like greatly impresses senior management, and leads to an executive position.
Handsome with an uderstandably youthful exuberance, Josh is attractive to a female executive in is company, and the result is a romatic interlude which, due to his inexpereince, he is largely incapable of handling. Eventually, he shares his secret with her, but, at first, she doesn't believe him. As she gets a closer and closer look at his behavior, however, she comes to understand.
Finally, Josh finds the arcade machine that had granted his wish, and wished to have the orgiinal wish undone, returning to his mother after weeks away form home.
The real beauty of the movie lies in the realization that an adult that manages to maintain the exuberance of youth is one to be greatly envied, and while the means by which this message is conveyed is highly unconventional, the message is delivered with insight and clarity.