The tweenage characters in “The Kid Who Would be King” freely acknowledge that they’re living through an endless story, “The Hero With a Thousand Faces,” they’d say — if they were reading Joseph Campbell at 12.”

“We’re Han and Chewy, Frodo and Samwise!” the nerdy sidekick, gamely played by Dean Chaumoo, offers.

The Harry Potter, “Star Wars” and “Lord of the Rings” comparisons — made by the characters here — abound.

What writer-director Joe Cornish, of “Attack the Block” and “Adventures of Tintin” and “Ant-Man,” has cooked up is a story built on the same “Young hero’s quest” framework, one of the great stories of that narrative tradition — the story of King Arthur and the Sword in the Stone.

He’s leaning, not on J.K. Rowling or J.R.R. Tolkein’s best-sellers or George Lucas’s equally famous saga, but on the “brand” that preceded them all.

Check out the street where our young fatherless hero Alex (Louis Ashbourne Serkis, whose father is Andy Serkis) lives with him mum (Denise Gough). “Malory Court” is named for Sir Thomas Malory, author of “Le Morte d’Arthur,” the most famous account of the Age of Arthur.

Cornish relies on Western audiences’ memory of chivalry, swords in stones, ladies in lakes, “the Once and Future King” and Round Tables to deliver a dose of good clean fun — with violence and jokes and a social relevence so obvious even a child could see it.

In a time “When hearts are hollow and the land is lost and leaderless,” when snippets of newscasts play up the violence and division fomenting world wide, a boy with the courage to stand up to bullies, pure of heart and noble of purpose, is bound to run across an ancient sword, cemented and rebarred into a foundation piling on a demolition site.

Well, a British boy is bound to, anyway. That’s what “The Once and Future King” portends — that the sword and the Lady in the Lake will find a new leader when Britain desperately needs one. And none of these inbred Germans masquerading as Windsors will have any say in it.

Alex is always sticking up for best bud Bedders (Chaumoo), who is constantly getting picked on by Dungate School class creeps Kaye (Rhihanna Dorris) and Lance (Tom Taylor).

“Don’t be a hero,” the towering Lance sneers, “It’s not worth it.”

But Alex, who covets the “Knights of the Round Table” book his absent Dad left him, cannot help himself.

Which is why the sword choses him. Or so he’s told by the gawky, hand-waving/spell casting new nerd in school, “Mertin (Angue Imrie).” He’s chosen a name that will deflect any connection to his real identity.

Mertin is really Merlin, a wizard as old as time (or as Patrick Stewart, who classes up the show). He shows up in a stolen Led Zeppelin ’75 Tour t-shirt and utterly upends Alex’s world.

“The penumbra between light and dark” is threatened, Merlin intones. And Alex and Bedders have to put things to right.

As the sword has made its choice, Alex must take it up and commission an order of knights and keep the evil Morgana (Rebecca Ferguson) from ascending from the underworld where she’s been imprisoned and enslaving humanity.

The minx.

I used the word “clean” in describing “Would be King” because Cornish has conjured up an Arthurian vision that is free from the clutter of the Hobbit and Harry Potter pictures. Even though there are some cool effects and monsters (fragile flaming wraith-horsemen) to battle, there’s none of this standing around and gawking at this or that “Fantastic Beast.”

Cornish relies on the viewer knowing the bare bones of the story he is riffing on and takes off from there.

And he uses that’s story deep messages, about chivalry and loyalty, the lure of adventure and necessity of compromise and coalition building, to teach his young audience (and those kids’ parents) about how to mend a “divided world.”

Who are the first recruits Alex rounds up for his quest? The school bullies. He is not the only one with a quest, a character arc. The little thugs have to find something nobler in their souls before they can become true knights.

What gets a laugh from any and all of them every time the phrase is used? “The Sword in the Stone.”

Merlin, in either his young Angus Imrie form or wizened, befuddled Patrick Stewart guise, is a goofy delight, sneezing in a cloud of feathers every time he transforms into his spirit animal (an owl), showing up as Old Man Patrick Stewart for the sake of credibility and gravitas, every now and then.

It’s all very English, from its grey skies and cute/posh accents (shared by a diverse cast) to the sort or wordplay the script trots out.

Merlin, in human form, laments his ability to get around in owl form in modern Brittainia.

“Are there NO unglazed windows or unblocked chimneys in this GOD forsaken country!”

The Uther Pendragon and Arthur story, the original “Sword in the Stone” tale, is told in animated form over the opening credits — a nice touch.

The kids are mostly just OK, not the charismatic, dazzling future stars Warner Brothers rounded up for the Harry Potter movies. Ferguson, of the last “Mission: Impossible” movie, makes an adequate villain, not a shake-in-your-boots terror/seductress that Morgana can be.

See the young Helen Mirren’s turn in John Boorman’s timeless “Excalibur” to see what a real fury looks and sounds like.

The few effects are sharp and crackling, though the action beats seem to play out at half-speed and are spread too far apart. Cornish makes the Lady in the Lake sticking her chain-mailed hand out of the water more the object of comedy (lakes, bathtubs) than awe-inspiring or thrilling.

And the movie, clocking in at over two hours, could use a few more thrills, heart-touching moments or those welling-with-pride “There will always be an England” touchstones. You know, like “Excalibur,” which had plenty of those, all scored with Wagnerian overtures or Orff’s “Carmina Burana.”

But “Kid Who Would Be King” is still an engagingly topical and smart fantasy film for kids, “good clean fun” that benefits more from “clean” than the creators of Hogwarts and Mordor or The Empire would ever guess.

MPAA Rating: PG for fantasy action violence, scary images, thematic elements including some bullying, and language |

Cast: Louis Ashbourne Serkis, Rebecca Ferguson, Patrick Stewart, Rhianna Dorris, Denise Gough, Dean Chaumoo

Credits: Written and directed by Joe Cornish. A 20th Century Fox release.

Running time: 2:05