At a rehearsal for Utah Opera’s “The Little Prince,” Nitai Fluchel and Jared Bybee face off in a fight that sets a theme through the whole story: adult “seriousness” versus childlike dreams.

Fluchel’s Prince and Bybee’s Pilot scowl at each other over schematics of a plane that the parched and hungry Pilot has crashed in the desert. The child Prince appears at the disaster scene, claiming to hail from a tiny asteroid and urgently begging the Pilot for a drawing of a sheep that will inhabit his fantastical world.

“Don’t bother me now! I’m working on something serious!” Bybee sings in irritation.

“Get mad at him!” director Tara Faircloth instructs 11-year-old Fluchel, who briefly meets Bybee’s grown-up glare.

A second later, both actors’ faces begin quivering in inevitable smirks.

“Don’t laugh!” Faircloth yelps futilely.

But Fluchel and Bybee became buddies early in the rehearsal process. It takes a few giggles to drill down to the serious moments — appropriate for an opera whose source material, the 1943 novella by Antoine de Saint-Exupéry, innovatively blurred the lines between children’s and adults’ literature.

The story traces The Little Prince’s life on his asteroid and his encounters with plant and animal characters on Earth, but the fantasy is laced with social critiques.

Some laughter also helps bridge the gap between a fifth-grader whose only previous opera role was as a goldfish in a school production (“One line — and I couldn’t remember everything”) and Bybee, a leading baritone whose credits include solo performances at Lincoln Center, Carnegie Hall and the Kennedy Center.

“The Little Prince,” which opens Saturday at the Capitol Theatre, features the largest role ever held by a child in a Utah Opera production, confirmed Melanie Malinka, musical director of the Madeleine Choir School.

The school, which often partners with Utah Symphony | Utah Opera, is supplying the 20-voice children’s chorus for “The Little Prince” and has helped prepare Fluchel for the title role. He’s been excused from some classes in order to get to rehearsals.

“When it’s done,” he said on a recent break, with less than an hour for dinner, “I’m going to be a lot less busy."

Singing the music of composer Rachel Portman and librettist Nicholas Wright — “mature but approachable,” Malinka describes it — is not terribly hard for Fluchel. His years at the Madeleine Choir School have prepared his voice and ear for that, he says.

He says the hardest part of singing opera is timing his entrances — in rehearsal, he bobs his knees in time with the pianist and focuses like any professional, internalizing the tempos and rhythms of the measures that will cue his lines.

Acting, however, is a new world — from taking stage direction to developing a convincing stage laugh.

Bybee and Fluchel rehearse the moment when the Pilot reconciles with the Prince after dismissing the child’s need for an imaginary sheep. Faircloth tells Fluchel to pivot from a crouch on the floor and throw his arms around Bybee, who is kneeling.

After a few run-throughs ending in tepid hugs, Faircloth instructs Fluchel to “turn around and grab him like he’s a life raft.”

Fluchel spins and flails his arms before losing his balance. Bybee tips over, too, and the giggles return.

“OK, let’s do that one more awkward time,” Faircloth says.

Weeks later, the costumes and sets envisioned by New York designer Jacob A. Climer have been created by the Utah Opera Production Studios — their look inspired by World War II-era Long Island, where Saint-Exupéry wrote the novella. Costumes evoke the period with jodhpurs and elegant calot hats; the action occurs within a study, with walls that move out to reveal the world of the story, the sand of the novella’s desert landscape replaced by dunes of paper, imagined as book pages.

And by now, Fluchel says, the scenes have been practiced to muscle memory, and he can inhabit the character even while remembering the libretto, hitting the notes, counting down his entries and making his way to the right part of the stage.

“When we start a scene,” he says, “I feel like the Little Prince.”

Seeing “The Little Prince”

Antoine de Saint-Exupéry’s classic novella, “The Little Prince,” is transformed into opera by Academy Award-winning composer Rachel Portman and playwright Nicholas Wright. Conductor James Lowe previously conducted “The Little Prince” at Washington National Opera.

When • Saturday, Jan. 19, 7:30 p.m.; Monday and Wednesday, Jan. 21 and 23, 7 p.m.; Friday, Jan. 25, 7:30 p.m.; Sunday, Jan. 27, 2 p.m.

Where • Capitol Theatre, 50 W. 200 South, Salt Lake City

Running time • Approximately two hours with one 20-minute intermission

Before and after • Utah Opera principal coach Carol Anderson offers a free prelude lecture one hour before curtain time. Artistic Director Christopher McBeth holds a free question-and-answer session after each performance.

Tickets • $29-$108 ($15 for students); utahopera.org