The ‘Shazam!’ star plays the title role in this live-action/animated retelling of Crockett Johnson’s classic children’s book, also featuring Lil Rel Howery and Zooey Deschanel.

The first few minutes of Harold and the Purple Crayon feature charming hand-drawn animation very much in the style of the 1955 classic children’s picture book by Crockett Johnson, making it easy to see why it’s still popular nearly 70 years later. In the original story, Harold was just a young boy, creating a wonderful world for himself thanks to his magic crayon. Unfortunately, in the new big screen, live-action/animated adaptation directed by Carlos Saldanha (Ferdinand, Rio, Ice Age), he’s all grown up. And despite the appeal of star Zachary Levi, it’s unlikely the film will have the same staying power.

David Guion and Michael Handelman’s screenplay has Harold, eager to experience what life has to offer outside his animated confines, drawing a door marked “Real World” and stepping through it. He emerges in the form of the strapping Levi, who looks rather silly walking around a city park in his onesie, which, no doubt in deference to the PG rating, is size-appropriate. He’s quickly followed by his cartoon friend Moose and then later by Porcupine, embodied by Lil Rel Howery and Tanya Reynolds (Sex Education) respectively.

Needless to say, Harold and Mel hit it off; the youngster identifies with Harold since he has an invisible friend named Carl. Mel attempts to help the duo find their old man, which leads to the inevitable farcical situations as Harold uses his magic crayon to create all sorts of objects, including a plane for them to fly around the city bearing a message beseeching old men to call a phone number that turns out to be Terry’s.

Complicating things even further is the story’s necessary villain, Gary (Jermaine Clement, easily stealing every scene with his hilarious delivery), a librarian with a major crush on Terry, who’s written a 700-page fantasy novel that’s clearly destined never to be published. When he finally becomes aware of the power of Harold’s crayon, he uses a purloined portion of it to attempt to fulfill his romantic and literary dreams. It all leads to an elaborate drawing duel in a local park, filmed as a parody of Sergio Leone’s spaghetti Westerns.

That sequence in particular will tickle the very small fry who are obviously the target audience, and it’s reasonable to assume that they’ll enjoy many of the other silly antics, especially the animal creatures drawn by Harold and Mel (when we finally get to see Carl, he resembles a crocodile with a flowing mane and wings). Adults, on the other hand, will spend much of their time scrolling on their phones since the humor is very much of the juvenile slapstick sort.

Howery makes an amusing foil (there’s definitely a Laurel and Hardy vibe between them), but the moose-turned-human idea doesn’t yield much comic fruit. Reynolds, however, is a delight, her spiky hair providing a visual correlative to a porcupine’s quills; she proves very funny when her character gleefully discovers the advantages of opposable thumbs.

Needless to say, everything turns out all right in the end, especially as told to us in the dulcet tones of narrator Alfred Molina — the aural onscreen version of the book’s author, treated in reverential fashion. It’s also nice that the film throws in a few sly homages to the Tom Hanks classic, Big, to which it owes an obvious debt. But it’s hard not to wish that in the future, Harold will stick to the cartoon world where he belongs.