Parenthood isn’t for the faint of heart.

Sleepless nights. Sudden illnesses. Bills atop bills. The Terrible Twos (and threes).

The parents at the heart of “The Unbreakable Boy” face two additional layers to family life. Their adorable son is autistic and suffers from “brittle bone” disease.

Their fact-based journey fuels a sobering look at parenthood. Yes, the “Oz Man” is the heart of the film, but Zachary Levi’s character offers an inspirational look at a flawed but fearless parent.

The charming courtship of Scott (Zachary Levi) and Teresa (Meghann Fahy, “The White Lotus”) gets an unexpected jolt. She’s pregnant, and the couple decides to move in together to care for their baby.

That’s Austin (Jacob Laval, excellent), an adorable lad with dueling medical conditions. He’s autistic, something the budding couple didn’t realize for some time. He also inherited his mother’s genetic condition leaving him prone to broken bones.

It happens so often that Austin’s narration ticks them off like minor achievements.

It’s enough to leave any parent woozy, Scott included. He’s comforted in two wildly different ways. He has an imaginary friend from his childhood named Joe (Drew Powell), a storytelling gimmick that shouldn’t work but often does, and beautifully so.

And Scott drinks when the stress becomes insurmountable.

The latter causes the most problems, naturally, and it’s one way “Unbreakable Boy” disappoints. Scott’s descent into alcoholism is too tidy and inconsistent to generate dramatic tension. The film’s PG rating keeps some grit off-screen, an understandable approach given the story’s feel-good bona fides.

Audiences of all ages will savor Austin’s joie de vivre.

We know Levi mostly for sweet, oversized roles (think “Shazam!), but he delivers an understated turn as a parent in crisis. Much of his pain is internalized, which makes those acting decisions wise.

Director Jon Gunn (“Ordinary Angels”), in turn, wrangles the tonal shifts with authority. It’s OK to relish Austin’s flights of fancy while processing his parents’ fear he’ll end up back in the hospital.

Or worse.

Patricia Heaton deserves more screen time as Scott’s mother, a no-nonsense type who looms large over his psyche. She’s maternal yet cold, a combination that could have been explored in a more nourishing fashion.

Peter Facinelli also feels underserved as Preacher Rick, a calming influence on Scott’s life. The “Twilight” alum offers the film’s faith-kissed elements, a hint at how faith becomes the most valuable element in Scott’s potential salvation.

Other story arcs deliver unexpected results, like the bully targeting Austin’s younger brother (Gavin Warren). 

Yes, “The Unbreakable Boy’ hits some predictable notes, but it does so with consistency and heart. Credit young Laval for holding the film together. Had his performance been too sticky-sweet this “Boy” would keep us at arm’s distance.

That’s hardly the case in this sweet and soulful drama.

HiT or Miss: “The Unbreakable Boy” has its flaws, but the joys of watching a bright lad inspire friends and family alike more than make up for them.