Nobody who has lived their entire life in one country can fully understand the strange, intimate disruption of emigrating as a family. For a time, parents and children are united and equal in disorientation, the adults’ authority on hold as all parties mutually wander and fumble their way through new cultures, geographies and social circles — a shared rite of passage, cutting through separating decades. Eventually, everyone finds their feet, traditional roles are reasserted, and stable family life resumes — except when it doesn’t, as depicted in Léonor Serraille’s delicate but wrenching second feature “Mother and Son.” An unsentimental but stoically anguished portrait of a tough single mother and two vulnerable sons settling (or not) in France from the Ivory Coast, it shows how the immigrant experience can equally tighten the knot between parent and child, or permanently unravel it.

An unassumingly ambitious drama, plainly but poetically told in three columns of time over a period of 20 years, this is a confident advance for Serraille from her scrappier 2017 debut “Jeune Femme.” That vastly appealing single-character study won her the Camera d’Or at Cannes, and was driven by a vibrant, untidy feminism in the spirit of Phoebe Waller-Bridge or Lena Dunham. “Mother and Son” retains that quality in its complex, unidealized female protagonist — vibrantly played by Annabelle Lengronne — though its social outlook is more expansive and inclusive: Inspired by the life and roots of her children’s father, Serraille’s original screenplay embeds tacit, national-scale socioeconomic commentary in its intimate domestic story, though smartly avoids making blunt symbols of its sharp, specific characters.

In particular, thirtysomething Rose (Lengronne) isn’t presented as any kind of ennobled maternal martyr figure, but as a restless, funny, credibly imperfect woman to match the similarly textured heroine of “Jeune Femme.” (That film’s star, Laetitia Dosch, fleetingly returns here in a modest cameo.) We’re told the bare minimum of the backstory and circumstances that drive independent-minded Rose to leave her Abidjan home for Paris in the late 1980s, with her sons Jean (Sidy Foudana), aged 10, and five-year-old Ernest (Milan Doucansi) in tow. It’s clear enough that she’s after a better life for her children than the one that drove her to this decision.

A doting, playful parent, she’s also not above putting herself first from time to time, particularly when it serves her fun-loving nature and healthy sexual appetite. But Jean and Ernest roll with the punches, the former doubling as a dutiful guardian to his younger brother when required by Rose’s hotel-service job and nighttime exploits; less forgiving are the married relatives (Audrey Kouakou and Étienne Minoungou) putting the family up in their already cramped social-housing apartment in the Paris banlieues. When Rose enters an affair with married Frenchman Thierry (Thibaut Evrard), and he offers to move the family to his hometown of Rouen, she leaps at the opportunity for escape; being a subsidized mistress, she reckons, still offers better prospects than the advances of fellow immigrants (notably besotted charmer Jules Cesar, played by Jean-Christophe Folly) in Paris.

Inevitably, none of this works out too perfectly, which we surmise as the narrative leaps forward in two stages, by roughly a decade each time — the guiding perspective shifting from Rose to Jean (played as a 19-year-old by rising star Stéphane Bak), and finally to Ernest (Kenzo Sambin, and later Ahmed Sylla). (The film’s French title “Un petit frère,” translating as “A Little Brother,” gives a more pointed sense of the film’s crux.) It’s a simple, graceful structure, one that requires audiences to keep reacquainting themselves with the characters, and their fragile, evolving relationship to each other. The boys, with varying success, seek to plant roots in the land they now recognize as home, as their birth country recedes in both their memory and their spirit — even as white peers, with unthinking crassness, continually ask where they’re from. For Rose, meanwhile, a concrete sense of belonging eludes her as she cycles through homes and jobs and relationships, while her grounding identity as a mother is diminished by the sons spiraling away from her.

It’s an inevitable evolution, both for the characters and the film, though it’s hard not to miss the lively, salty, lit-fuse energy of Lengronne’s terrific performance when it no longer leads proceedings after the first third. That’s no slight on the unaffected, expertly cast young performers playing Jean and Ernest at various stages, though the increasingly anxious, recessive nature of these young men as they mature is reflected in the film’s escalating emotional reserve and permeating, just-under-the-skin sadness.

Serraille’s filmmaking, more sober and restrained than in “Jeune Femme,” works at the same temperature, with Hélène Louvart’s lovely, unfussy lensing never letting compositional beauty overwhelm the weathered, changing faces at the center of the shots. And there may be no more banal or intensely poignant image in the film than a stack of tupperware containers, filled-to-spilling with a mother’s carefully cooked stews and rice, hauled out of a carrier bag as a peace offering to a coolly disengaged child — a taste of home, though no longer recognized as such.