The most reliable form of blockbuster for Hollywood studios nowadays is the computer-animated kidflick. They flow into theatres on what seems a weekly basis, and good, bad or indifferent they do big business—a sign of the desperation of parents to find something to keep the children entertained. This week’s entry in the sweepstakes, “Rise of the Guardians,” falls in the middle of the pack. It’s hardly an instant classic, being too busy and derivative by half. But portions of it possess a lovely, ethereal charm, and visually it’s very impressive.

Based on a series of books (and a short film) by William Joyce, the script is predicated on the premise that a quartet of “imaginary” characters—Santa Claus (voiced by Alec Baldwin), the Easter Bunny (Hugh Jackman), the Tooth Fairy (Isla Fisher) and the mute Sandman—have been assigned the task of protecting the world’s children from the gloom that follows giving up faith in them. Their work is suddenly imperiled by the reappearance of Pitch Black (Jude Law), the Boogeyman, who aims to change things by destroying children’s belief in the Guardians and thus replace their dreams of sweetness and light—and their innate hope—with nightmares and fear.

Perceiving the danger is The Man in the Moon, a sort of deus ex caelo who instructs the Guardians that they must add a new member to their ranks—puckish Jack Frost (Chris Pine). But Frost, haunted by his inability to remember his life before emerging from a lake in his present form, and by the fact that he is barely known to the children whose winter antics he’s responsible for—at first refuses the invitation. But once he joins in the effort to defeat Pitch, he becomes the virtual point man in the effort, though he will have to overcome his own insecurities, which the villain is more than happy to take advantage of, to engineer their victory. The final confrontation involves a single child, a boy named Jamie (Dakota Goyo) with whom Jack had previously cavorted in the snow unseen and who becomes the last child on earth to believe in the Guardians. Of course, Jack earns the lad’s faith too—evidenced in the kid’s ability to see him—as well as the satisfying knowledge of where he came from.

It’s obvious, of course, that the central notion in the story—the dependence of the Guardians on the belief of children in them for their very existence—is modeled on the famous Tinkerbell episode toward the end of “Peter Pan.” Thankfully the audience isn’t asked to clap their hands if they believe—there are children onscreen to act as their surrogates in that respect—but the debt is certainly there.

In addition, “Rise of the Guardians,” like so many team movies, has a surfeit of characters, and not all of them are particularly endearing. The four original members are never as magical as intended. Santa, voiced like a Russian commissar by Baldwin, is less jolly than stentorian—even his sleigh, with its massive reindeer, seems like something out of a May Day parade—and the aggressive, pugnacious Bunny is, as voiced by Jackman, simply overbearing (when he appears pint-sized at the close, however, it’s cheekily amusing). As for the Tooth Fairy and Sandy the Sandman, they’re both rather tepid by comparison. It doesn’t help, either, that each of the three non-mute guardians is accompanied by an army of “cute” helpers—for Santa a bunch of triangular, bell-wearing elves (as well as the Yeti, who actually build the toys), for Bunny a bevy of eggs that stumble about on tiny legs, and for Toothy a passel of sweet fairies that do the actual leg (or wing) work. It’s though the filmmakers felt that every image had to be chock full of riotous movement, all made more busy by action that pops out at the audience in 3D, to hold the kiddies’ interest for more than two seconds.

Nor is the villain a particularly strong creation. Law’s purring, wheedling voice gives Pitch some distinction, but visually he’s just a topcoat-wearing dude accompanied by hordes of snarling black dogs, and the clouds of black smoke he’s able to conjure up don’t have much more magic in them than the glistening streaks of gold dust that Sandy uses to bring sleep to children.

There’s a good deal of compensation, however, in the material focusing on Frost, who’s voiced delicately by Pine (though one could have done without the constant bursts of laughter meant to inform us of how much fun he has flying around in the snow). With the undercurrent of fragility in his thin frame and vulnerability in his personality, Jack is certainly the most affecting, appealing character here, and it’s good that the film really focuses on him. As a solitary, moreover, he isn’t accompanied by a lot of irritating little critters. It’s a pity that the screenwriters have chosen to diminish him at the close by effectively borrowing—a kinder word than stealing—his departure from Jamie, the boy who’s saved the world of childhood, from “E.T.” Memories just aren’t that short.

So it’s for its quieter episodes—and the visual magic they inspire—rather than the louder, brasher ones that one can embrace “Rise of the Guardians.” Who would have thought that Jack Frost would have so outshone his far more illustrious fellow fantasy figures?