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Early on in this peculiar exercise in family-targeted fantasy, Dwayne “The Rock” Johnson, as an over-the-hill hockey player, tells an admiring, wide-eyed but tiny tyke who dreams of becoming a pro himself, “Lower your expectations.” It’s advice that anybody going to “Tooth Fairy” might well take to heart—though frankly you have to wonder how a movie with this title and star could engender high hopes in the first place. Though there are plenty of wings on display, it utterly fails to take flight.

The inspiration for the script, if you can call it that, apparently came from Tim Allen’s “Santa Clause” series, in which an ordinary guy had to assume the role of Mr. Claus. Here Derek Thompson (Johnson) is a once-star player reduced to being a minor-league team enforcer dubbed the tooth fairy because of his propensity for knocking incisors and molars out of opposing players. (You can tell it’s designed for kiddies when he slams some poor shmuck in the kisser, sending one of his teeth into the stratosphere, pristine and with nary a smidgen of blood to accompany it.)

Dissatisfied with the way his own life has gone, Derek’s a cynic, brutally honest in dashing kids’ fantasies (as his advice to that little fan demonstrates). And he goes too far when he tells little Tess (Destiny Grace Whitlock), the adorable daughter of Carly (Ashley Judd)—the woman he’s dating—that the tooth fairy is a myth. That cues tooth fairy godmother Randy (Julie Andrews) to summon him to the fairy realm to serve as a “real” member of her staff for a couple of weeks as punishment for his malfeasance.

The humor in the movie is supposed to come from watching Johnson, dressed up in wings and odd outfits, sneaking into houses to retrieve teeth under the tutelage of his “manager,” the wingless bureaucrat Tracy (Stephen Merchant). And the pathos is meant to derive from Derek’s efforts not only to overcome his cynicism and bond with Carly’s kids Tess and Randy (Chase Ellison), the initially hostile pre-teen to whom he needs to become a surrogate dad, but to recover his own dreams. It all comes down to his ability to believe, and to encourage others to do likewise—a motif that, given the fairy motif, has distinct echoes of the famous scene in “Peter Pan.”

But there’s very little similar magic at work in “Tooth Fairy.” There are a few mildly amusing moments involving amnesia powder and a handful of bright lines (the remnants, it seems, of the wit that Lowell Ganz and Babaloo Mandel were once known for). And Merchant has a gangly charm as the prissy bureaucrat, with a delivery that recalls John Oliver’s. But overall, things are just bland. That’s partially due to tepid writing and Michael Lembeck’s leaden direction.

But it also has to do with Johnson. He seems like an amiable lug, but his acting skill is about at the level of any professional wrestler—which is to say, not much. He tries hard, but even his screams when his wings appear and he finds himself dressed in a tutu have a hollow ring: fantasy like this has to be played with conviction if we’re going to buy into it—even if we’re kids ourselves—and Johnson simply lacks it. Still, it’s difficult to be too hard on him. What actor could make us believe in a story based on the premise that a big, tough hockey player would tolerate being acclaimed by a cheering crowd as a fairy, of whatever kind?

Otherwise the cast is given little opportunity to shine. It’s nice to see Judd freed from her string of awful action heroine parts, but she doesn’t do much with this sitcom-quality role but react, though she does have one good sequence involving that amnesia powder. Kids Ellison and Whitlock could also have stepped out a TV comedy—in their case on the Disney Channel or Nickelodeon—though they’re likable enough on that level (even if the boy’s talent-show finale is pretty gruesome, even by those standards). As for Andrews, her regal-persona schtick feels like nothing more than the continuation of her turn in “The Princess Diaries.”

“Tooth Fairy” has been given a candy-colored production, especially in the “fairy office” sequences, but neither the sets nor costumes are top-grade, and David Tattersall’s cinematography is no more than adequate. Meanwhile the score by the prolific George M. Clinton, as usual, italicizes every point in a futile attempt to generate laughs.

Family comedies starring erstwhile action stars don’t have a very good reputation—remember “Jingle All the Way”? Among the more modern examples, this one is better than Jackie Chan’s “The Spy Next Door” but worse than Vin Diesel’s “The Pacifier,” which means it doesn’t rank particularly high. And one can only hope it doesn’t serve as a precedent for, let’s say, John Cena following up “The Marine” with a fantasy in which he plays the Easter Bunny.