It’s not hard to see why some audience members walked out of a Sundance screening of A Lion in the House, a haunting documentary about children with cancer. Four hours of footage on any single theme is a lot to handle, but four hours of anguished families watching their kids undergo horribly invasive treatment for virulent forms of the disease — and then seeing some of them die anyway — is devastating. Lion is enough to test anyone’s belief in a benign deity, but it is essential viewing, not only as an antidote to the idiotically sentimentalized depictions of childhood cancer we see in most television and movie dramas, but for what it tells us about the way kids and parents bear up — or not — under adversity no one should have to experience.

In the movie, which airs June 21 and 22 on PBS, you’ll see no demon doctors, saintly parents or angelic little victims pining away prettily on snowy pillows. This sympathetic yet unflinching vérité film, directed by Steven Bognar and Julia Reichert, whose own teenage daughter went through a year of cancer treatment, is at once tactful and matter-of-factly graphic as it tracks the roller coasters of remission and relapse most families of pediatric cancer patients must navigate for years at a stretch. And though it might be a little worrying that the project was instigated by the chief oncologist of Cincinnati Children’s Hospital, where Bognar and Reichert spent the better part of six years following five kids from diagnosis through treatment to recovery or death, the film is no shill for the medical establishment. If anything, it’s a remarkably evenhanded, experiential account of the rapidly changing milieu of modern medicine from the point of view of the children, their parents and the medical teams assigned to their care. Among its many virtues, the film persuades you to withhold judgment on some pretty weird behavior.

The old cliché about cancer being the ultimate social leveler is made flesh in the radically disparate ethnic and socioeconomic circumstances of the young patients: Tim and Al, two charming and voluble black teenagers with devoted but cash-strapped single mothers; and — from rather more well-to-do backgrounds — Alex, a lively and willful 7-year-old curly-head; a thoughtful 6-year-old named Jen; and Justin, who’s almost 20 and is both the most visibly sick and the toughest fighter. Like the nurses who care for them, the movie treats them as kids, not as patients. And we get to know them really well, which is both rewarding and difficult to watch. As if the cancer and its often painful treatments weren’t enough, all have had to deal with related problems at home and school, yet they’re a remarkably resilient lot. The younger the children are, the more likely they are — as most little kids do — to take life as they find it, at least until the physical pain grows intolerable. The older ones, more sensitive to disfigurement and social rejection, have a harder time coming to terms. But it’s the parents and the doctors who find themselves in agony, in large measure because of enormous advances in cancer treatments that have significantly raised survival rates even as the rates of contraction have also slowly increased. The dilemmas they face are essentially the same as those that confront geriatric patients — survival can be prolonged (maybe) but at what cost? — only with the added tragic dimension that children, unlike old people, have yet to live their lives. Choice may be the solution, but it is also part of the problem, bringing impossible decisions that balance the possibility of a cure against incredible physical and emotional suffering, as well as the financial hardship when insurance money runs out. Every family we meet confronts this, but the critical case is that of Justin, who at 19 has been battling cancer for 10 years. An extraordinarily strong boy with a saving sense of humor, he cheats death time after time — and turns into a vegetable before our eyes. “We’ve cured his leukemia,” one of the medical staff harrowingly laments in a meeting. “But we’ve created a situation where he has no quality of life.” Watching Justin’s perennially smiling mother, who rarely leaves his bedside, push for more and more heroic measures as her son wastes away, I wanted to kill her. Yet by the end of the movie, having lived for a few hours with these families and their doctors, I understood that any of us who think we know how we’d act in their place are fooling ourselves, and that A Lion in the House has achieved no less than a redefinition, and a necessary complication, of heroism itself.

A LION IN THE HOUSE | Produced and directed by STEVEN BOGNAR and JULIA REICHERT | PBS, June 21 and 22, 9 p.m.

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