There’s a moment early in “Children of Syria,” filmmaker Marcel Mettelsiefen’s at-times harrowing but ultimately life-affirming PBS Frontline documentary of one family’s courage and resilience under fire, that says everything about how very young children — four, in this case — view injustice and right and wrong.

Four-year-old Sara is exploring the hollowed, abandoned houses of her neighborhood in Aleppo, Syria with her older sister Helen, who at age ten has become the de facto parent and guardian of the family, if only temporarily.

Sara has found some stuffed toys, left behind by a neighbor family in their hurry to flee the battered, war-scarred city. She wants to take them home with her, especially a stuffed bear, who she instantly adores. She has hardly any toys of her own, and certainly not this nice.

“No, you shouldn’t take them,” he older sister tells her. “It’s shameful. It’s wrong.”

“But they are really pretty, aren’t they?” the younger girl says, and then decides, clutching them under her arm defiantly. “Let’s go.”

Moments later, her father Abu Ali, an engineer who’s joined the Free Syrian Army rebel group in their revolt against the government of Basher Al-Assad, confiscates the toy and berates her for taking something that didn’t belong to her. When things are better, he promises, “We’ll buy you a toy.”

She starts to cry, because she knows the stuffed bear needs a home and, even at her age, she suspects the neighbor family will never come home again.

“Children of Syria” is strong stuff, both as documentary filmmaking and as a testament to the human spirit.  It premieres on PBS at 10 p.m. ET Tuesday (4/19). (Check local listings)

The refugee crisis is headline news these days, a seemingly intractable problem with many sides and no easy solutions. The crisis has been allowed to metastasize and the ripple effects have taken on worldwide implications. What the world doesn’t need now is yet another obvious, pat documentary designed solely to tug the viewers’ heart strings and manipulate emotions with trite homilies or, worse, strident, bullying narration.

“Children of Syria” is not that, thankfully. It’s deeply layered, and yet objective in approach. As much as any film about war and displacement can be, it’s quiet and understated, rather than loud and in-your-face. It leaves it to the viewer to decide right from wrong, and there are moments in it that are surprisingly peaceful and poignant.

Even in the pantheon of great contemporary documentary filmmakers — Andrew Jarecki, Alex Gibney, D.A. Pennebaker, Errol Morris — “Children of Syria” represents documentary filmmaking in its purest form. Over a four-year period, filmmaker Mettelsiefen, a German-born war correspondent, photojournalist and BAFTA award-winning filmmaker, spent time with a family under siege in Aleppo: mother, father, an older son and three daughters, Helen, 10, Farah, 7 and Sara, 4, when the film begins in 2012.

Over the course of the next four years, Mettelsiefen checks back in — first as the revolt against Al-Assad has reached a bitter stalemate, then as ISIS fighters infiltrate the city and starts to execute fellow revolutionaries who don’t adhere to their own twisted brand of religious extremism. The film jumps ahead a year — Abu Ali has been seized by ISIS fighters, never to be seen again — and Hala, the girls’ mother, finally decides to flee the city, taking what’s left of her family with her, to the border with Turkey, through territory that’s claimed by both ISIS and the Assad regime, neither of which are kindly disposed to refugee families representing “the other.”

The film then jumps ahead to present day, to a small, mountain town in Germany, where the broken family is trying to mend while trying to assimilate into a new culture and way of life.

“Children of Syria” runs just under an hour, and yet it tells the story of a lifetime, with more nuance and human detail than films twice as long.

It’s hard to put into words just how provocative and profound this film is. It’s hard, too, to imagine different viewers seeing this film the same way. It’s surprisingly personal, and is likely to touch different viewers in different ways. Left to form your own judgment, you’re not always comfortable by what you find.

I found myself hating — loathing, even — the family’s father for so selfishly putting his own children in harm’s way, and yet there’s a moment in the film where he candidly admits as much. His wife Hala couldn’t conceive for eight years, he says; that’s why his children are so special to him.

“I am the reason for destroying my children’s future right now…” he says sadly. “I have sacrificed my children for the revolution.”

They will possibly pay with their lives, he realizes.

“Here they could get killed at any moment. I hope this will count. It’s all a sacrifice for the revolution.”

A year later, he has been seized by ISIS and vanished. The girls, who used to react to the sound of exploding bombs and missiles with excitement bordering on glee — look, fireworks! — now cry uncontrollably whenever a shell detonates nearby.

Hala is beside herself: What’s the matter with you, she tells them. You never used to cry like this.

“I’m not scared of anything any more,” Helen says. She’s now 11, but she looks more like 14. She has aged considerably, grown up before her time.

“There’s no need to be scared of anything because there’s nothing left in our life,” she continues. “Sometimes I get a moment of hope that our father is coming back. And sometimes I lose hope that my father is ever coming back. Then I cry a lot. My brain sometimes tells me this, and then something else, and my conscience tortures me. I don’t know what’s happening to me.

“We suffered a lot -- a lot.”

Hala has had it. “Daesh,” the Arab acronym for ISIS, has destroyed her family’s lives, she says angrily. The revolution against Assad is now an afterthought. 

“Our country has been destroyed. Everything good has gone, everything. So I’ve decided to leave.”

And it’s here where the film becomes not just gripping but emotionally wrenching and timely all in one. She flees to Turkey — not an easy trip — and then gets a stroke of luck. Germany has agreed to take in 20,000 refugees — the number is now closer to a million — and, for whatever reason, her family has been granted asylum. She is one of the lucky few.

“What are you going to do in Germany,” the filmmaker asks the children, each one in turn.

“I will play,” Sara, the youngest, says. “What else would I do?”

“What will I do?” Helen says. “I’ll just stay at home.”

“You’ll study,” her mother tells her determinedly.

“I will meet people,” Helen adds hopefully. “I don’t know. I don’t know how to speak French.”

Farah, now 8, has drawn a childlike map of Turkey and what little of Europe she knows.

Why did you make this drawing, the filmmakers ask her.

“So that dad might see it and come to us in Germany,” she replies.

Hala knows better, but she has yet to find the strength to tell her children.

And then it is January 2016 — this year, just four short months ago, and the family is in a small mountain town known, according to literature from the town’s chamber of commerce, “for its elderly population.”

The contrast of a clean, neat, tidy, law-abiding town in Bavaria and the shattered ruin of Aleppo, Syria could not be more striking. 

Helen — who volunteered as a field worker in a refugee camp and is now volunteering in a community-based assimilation center for new migrants to Germany — has become a typical teenager, and the transformation is both remarkable and heartwarming to see. The girl who once said she’d lost hope, that there was nothing left in her life, now has a whole future of possibilities opening up before her.

Her siblings are adapting to their new lives, in their own personal, often different ways, her younger sisters more comfortably, perhaps, than her older brother.

It’s not all The Sound of Music. Right-wing extremists from surrounding towns — skinheads, for lack of a better word — have been threatening the migrants, and the mood in Germany has darkened since 20,000 refugees became closer to half a million.

Even so, “Children of Syria” is full of grace notes and poetry, often when least expected. It’s a grueling journey, not always easy to watch, and there are moments that will make you deeply angry.

And yet, when it flies, it soars. It is, quite simply, unforgettable. “Children of Syria” is one of the most remarkable films about children and war ever made.