Fraternal writer-directors Jean-Pierre and Luc Dardenne bring the neo-realist approach they earlier demonstrated in such extraordinary films as “La Promesse” and “Rosetta” to the tale of a small-time street hustler, his girlfriend and their infant son in “L’Enfant,” though without quite the same degree of success. Told without sentiment or an excess of didacticism, this story of redemption among the urban underclass carries considerable power but never becomes a truly searing experience.

Jeremie Renier plays Bruno, a mop-haired, bantam-weight petty thief and panhandler working the streets of Seraing, a shabby Belgian industrial town. Dismissing a regular job as something for fools, he keeps things together by stealing purses and cameras, which he then pawns, in cahoots with Steve (Jeremie Segard), a cocky young kid who borrows his brother’s motorbike so they can make a quick getaway. As the picture opens, Bruno’s girlfriend Sonia (Deborah Francois) returns with their new-born son Jimmy, and the duo proceeds to begin applying for the government aid that will help them keep their dumpy apartment. But Bruno has different ideas. Without telling Sonia, he barters away Jimmy to an underground group specializing in illegal adoptions, only to find that she’s appalled and tosses him out. He gets back the infant, but in the process incurs a big debt to the purchasers, who demand that he pay them the profit they’d have made on the transaction and show a readiness to resort to violence if he doesn’t. Meanwhile the disappearance of the child, and Sonia’s collapse at the news, have gotten the police involved, and an attempt to get the money he needs to pay off his creditors goes awry, ending in a chase in which Steve almost dies. The collapse of his world forces Bruno finally to confront the reality of his life, come to terms with his actions and accept responsibility for them.

The title of “L’Enfant” obviously refers to Jimmy, but it relates to the father as well–a man who’s effectively never grown up himself, who acts on impulse, who has no sense of the effect of his acts. The film is really the story of his journey from emotional infancy to at least the beginnings of maturity, and Renier plays the young man without overly sentimentalizing him or seeking to make him likable; some will dismiss the performance as flat, but the lack of interior life is what the character is all about. Francois, meanwhile, catches the rage of Sonia’s maternal instinct well, and Segard is very credible as a kid who wrongly thinks himself invincible. While generally opting for a gritty, naturalistic approach (abetted by the cinema verite style of cinematographer Alain Marcoen), the Dardennes manage to infuse some of the set pieces with considerable tension, most notably those in which Bruno passes the child to the unseen purchasers in an abandoned building and then retrieves him from them in a shuttered garage, and another in which he and his young accomplice try to escape with the loot after snatching a woman’s bag but are chased to the river front by some good Samaritans. The technical side of the film, in keeping with the neo-realist slant, is undemonstrative, and the lack of background music maintains the almost documentary feel.

“L’Enfant” doesn’t carry quite the emotional punch of “La Promesse” or “Rosetta,” but it represents a solid addition to the filmmakers’ cycle of films about members of the economic under-class being tested by sharp ethical dilemmas. Though less compelling than those earlier pictures, by melding social criticism with incisive personal drama, it brings home the reality of life for many in the modern city and the necessity–and difficulty–of developing a moral compass to navigate that landscape; and the deceptive simplicity of the approach bolsters its effectiveness.