Not every movie deserves an exclamation point. “Airplane!”, yes. “Moulin Rouge!”, not so much.

“Shazam!” earns its punctuation through unrelenting, gee-whiz cheerfulness. Fueled by nerd energy and sold by a goofy cast, this superhero spin-off carves its own path through the usual comic-book material.

Our hero is adolescent Billy Batson (Asher Angel), an unhappy orphan assigned to his umpteenth Philadelphia foster home.

Billy is tapped by destiny — or, to be specific, by an ancient gray-bearded wizard (Djimon Hounsou) with a magical stick — and acquires superpowers. If he merely says the word “shazam” out loud, he can turn himself into an indestructible hero, complete with cape and tights.

In big-boy guise, he’s played by Zachary Levi (from TV’s “Chuck”), a 38-year-old actor who convinces us he’s really 15. The film explicitly acknowledges its similarity to “Big,” another film about a lad who suddenly finds himself in an adult body.

Billy isn’t the only person in the universe with special skills: We meet another such kid in the movie’s jarringly creeped-out prologue. That boy grows up to be resentful Thaddeus Sivana (“Kingsmen” veteran Mark Strong), a supervillain with a glowing glass eye and an entourage of hideous sidekick demons.

As sidekicks go, Billy has the edge. Fellow foster kid Freddy (funny, whiny Jack Dylan Grazer, from “It”) knows everything there is to know about superheroes — which makes him exactly the target audience member for this movie.

As Freddy would point out, although this superhero’s comic-book origins are tied to a character called Captain Marvel (this is very complicated to explain), “Shazam!” is not a part of the Marvel universe. This is a DC Comics movie, but it makes almost no effort to connect itself to the broader DC world, which is a relief.

A few moments of blithe destruction don’t quite go with the otherwise jaunty tone — one corporate board meeting plays as darkly as something out of “RoboCop.” And director David F. Sandberg dawdles a bit before we get to the first “shazam” moment (there’s no reason this movie needs to be 132 minutes long).

Along with the breezy slapstick, what “Shazam!” does best is sketch its little misfit community. Billy’s new pals from the foster home play an increasingly large role as the action climaxes — at which point you realize the film is a wish-fulfillment about lost kids who secretly harbor superpowers, even if they’re getting beat up at school the rest of the time. That’s a fantasy at the heart of most comic books, and jovially earned here.

“Shazam!” (3 stars)

An orphan adolescent (Asher Angel) gains the ability to become an adult superhero (Zachary Levi), merely by uttering the word “shazam.” The movie owes a lot to “Big,” but earns its own fun through its unrelenting, gee-whiz cheerfulness. A jovial cast (including supervillain Mark Strong) helps put over this lightweight lark from the DC Comics world.

Rating: PG-13, for violence, language

Showing: Alderwood Mall, Everett Stadium, Galaxy Monroe, Marysville, Stanwood Cinemas, Meridian, Oak Tree, Pacific Place, Thornton Place, Woodinville, Cascade Mall, Blue Fox, Oak Harbor Plaza