The sheer existence of this live-action adaptation of the classic children’s book “Harold and the Purple Crayon” inspires a number of basic questions. Who is this for? The book by Crockett Jensen, published in 1955, is aimed at ages 3 and up, but the film, starring a mostly adult cast, skews older. But the premise still feels too thin and juvenile to grab audiences of any age. So, where, when and specifically what algorithm decided this film would be a lucrative endeavor?

Directed by “Ice Age,” “Rio” and “Ferdinand” director Carlos Saldanha, written by David Guion and Michael Handelman, the approach to adapting the beloved book is a curious one. We know the story and the iconography: a toddler in a onesie who uses his imagination and a purple crayon to make his world more exciting. In the film, our protagonist is now an adult Harold (Zachary Levi), who still lives in his 2D world with his friends that he drew, Moose (Lil Rel Howery) and Porcupine (Tanya Reynolds). Despite being in his mid-40s, he’s still quite childlike, and overly attached to his only parental figure, “the narrator” (voiced by Alfred Molina), whom he calls the “Old Man.” When one day the Old Man’s voice goes away, Harold draws himself a door to the real world in order to find him.

Why the decision was made to feature a middle-age Harold likely has to do with Levi’s willingness — or desire — to star as a childlike man, as he has done previously in both “Shazam” films. His version of Harold is a cross between Tom Hanks in “Big,” and another children’s book icon, Amelia Bedelia. Harold knows nothing of “the real world,” including irony, idioms or brands, and like Amelia, he takes everything literally — a problem when he’s wielding a crayon that can draw anything into existence.

For some reason, when they transfer into the real world, Moose and Porcupine become human. The trio cause light havoc, glomming onto a single mom, Terry (Zooey Deschanel), and her son Mel (Benjamin Bottani). Harold, Moose and Porcupine need help finding the Old Man, and then they get involved with Terry’s issues, too.

Things are looking so, so dire in this world, and then a savior arises out of nowhere. It is the East, and Jemaine Clement is the sun. Clement plays Library Gary, a writer of romance-fantasy fiction, who has a crush on Terry.

Even though his pompous author character is a bit close to his role in 2009’s “Gentleman Broncos,” Clement proves to be a breath of fresh air and a decent adversary. If Harold uses his crayon to pull planes and pies out of thin air, Gary has far more nefarious intentions, using the crayon to summon up his fantasy world, complete with powerful magical staffs, a floor made of lava and scantily clad maidens.

It’s only when Clement brings his flair that this film has anything worth paying attention to; he’s the dash of acid that tempers this otherwise saccharine story about embracing imagination. The less we focus on what Levi, Howery and Reynolds are doing, the better.

MPA rating: PG (for mild action and thematic elements)

Running time: 1:32

How to watch: In theaters