The stripped-down aesthetic principles, compassionate humanism and naturalistic purity in the films of Jean-Pierre and Luc Dardenne make their body of work uncommonly cohesive. It’s easy to be glib about the influential Belgian brothers and say you know exactly what you’re getting with a new Dardenne film — much like their social realist counterpart across the North Sea, Ken Loach, whose films they began helping to produce in 2009. But anticipating the form, the political leanings or broad thematic concerns of a movie is not the same as knowing in advance where it will take you, what kind of marginalized lives it will illuminate.

Ever since their international breakthrough in the 1990s with La Promesse and Rosetta, there’s always been the capacity to surprise in a Dardenne movie. Their latest, Young Mothers (Jeunes Mères), is the filmmakers’ most surprising work in years. It provides unfiltered emotional access to the anxieties and hopes of five vulnerable working-class teenage women and the babies requiring their love and care, often when they can barely care for themselves.

The project was hatched out of a visit by the Dardennes to a maternal support home near Liège, with the initial aim of developing a story about one young mother struggling to connect with her baby. But they were so struck by what they witnessed there — among the mothers as well as the nursing, counseling and administrative staff — that they expanded their plans to build a multicharacter ensemble piece.

That alone marks a shift for the writer-directors, whose work tends predominantly to lock in on one or two main characters. It also allows them to draw even more than usual on their background in documentary. Young Mothers is closer to docu-fiction than any of their recent work. It follows the struggles of four women, three of them with newborns and one who’s pregnant with a looming due date, plus a fifth whose stay at the shelter is nearing its end.

Just two weeks away from giving birth, Jessica (Babette Verbeek) waits in an agitated state at a bus stop where she has organized to meet her biological mother Morgane (India Hair), who gave her up for adoption when she was younger than her daughter is now. Both before and after the arrival of her baby, Jessica longs to understand the reasoning behind her mother’s decision, and to know if she ever felt remorse.

Perla (Lucie Laruelle) has given birth to a son while the boy’s father, Robin (Gunter Duret), was in juvenile detention. She brings him a spliff to celebrate his release, but Robin shows little affection for her and barely even looks at their child. While Perla has signed out of the shelter for several hours, expecting to spend the day with him, Robin can’t get away fast enough. Perla faints when she gets back, and another young mother, Julie (Elsa Houben), massages her to knead the numbness out of her body.

Fifteen-year-old Ariane (Janaina Halloy Fokan) wants to put her infant daughter in foster care and finish school. Her mother Nathalie (Christelle Cornil), who talked her out of having an abortion, is against that plan, insisting she can help raise the child. But Nathalie is a drunk who has been in an abusive relationship with a violent man. At first, she coaxes Ariane to visit by assuring her that she has quit drinking and dumped the guy, but there are signs that indicate otherwise. Growing impatient with her daughter’s rebukes, Nathalie snaps, “He hit me worse than he hit you.”

Julie and her baby’s sweet-natured father, Dylan (Jef Jacobs), are both recovering addicts. They leave their young daughter at a childcare facility while they go across town to see a subsidized apartment where they hope to live as a family. Dylan, a baker’s apprentice, wants to marry her; their journey on his moped is one of the film’s loveliest sequences, an image of freedom and happiness that suggests such a life might be within reach. But there are hiccups.

Setbacks are as much a part of these women’s realities as their tentative steps forward, yearning to carve out better lives for themselves and their children. One incentive to keep trying is the success of Naïma (Samia Hilmi), who is preparing to move with her child into their own flat and is on track to secure a job as a railway ticket inspector. Her sendoff from the shelter, with cake served outside in the garden, is one of many affecting displays of solidarity.

Others have a bumpier path: Julie relapses into drug use and anxiety attacks; Perla refuses to read the obvious signs that Robin has no interest in settling down with her or becoming a hands-on father; Jessica keeps hitting a wall with her mother and has a hostile encounter with the unsympathetic parents of her baby’s father, who run what appears to be a successful gym. They demand to know what she wants from their son, insisting that she’s to blame for her situation since she declined to have the abortion they offered to pay for.

The filmmakers thread these stories seamlessly into a larger picture that balances despair with moments that point cautiously toward a more stable future. There’s never a false note from the young actors, all of whom have deeply moving scenes. But Young Mothers is also captivating when it’s simply taking in the quotidian responsibilities of new parenthood — feeding, diaper changing, bathtime — or when it catches an expression of wonder or joy as a mother gazes into the tiny face of the child she has created.

DP Benoît Dervaux’s camera is always attentive, never intrusive or fussy, and the use of only available light adds to the documentary-like authenticity of the stories.

Possibly the single most gorgeous moment in the movie happens when one of the mothers, bracing for the wrenching separation of putting her baby into foster care, straps the infant into a car seat. If you don’t melt when you see the blissful smile that spreads across the baby’s adorable face and lights up her eyes, I suspect you’re a terrible person.

As attuned as they are to the harsh experiences of characters living bare-bones existences on the fringes of society, the Dardennes have never been doom-peddling fatalists.

That aspect is clear in a number of beautiful forward-facing scenes — Ariane writing a letter for her daughter to read when she turns 18; Jessica breaking through and being able to communicate with Morgane when her dogged determination pays off; Perla having a blowup fight with her older half-sister, Angèle (Joely Mbundu), but then reconciling with genuine warmth and an offer of support; and especially, Julie and Dylan taking their baby to visit a former music teacher who helped them both.

The Dardennes are not in the business of offering easy fixes for their characters’ difficulties. But when the teacher sits at the piano to begin the child’s introduction to music, Mozart’s “Rondo a la Turca” sounds like a hymn of triumphant resilience and elation.