The Dardenne brothers discuss their latest film The Kid With a Bike.

What would it be like to be the first three-time Golden Palm winners in Cannes history?” It was the question Belgium’s Dardenne brothers were asked as regularly as a gong at the last festival. Their newest film, Le Gamin au Vélo (The Kid with a Bike), was adored by critics and audiences. It’s a hugely touching redemption tale about a 12-year-old boy, rejected by his father, who is rescued from the temptations of crime and delinquency by a caring young woman. Think early Truffaut with a sobering dash of Bresson.

In the event, they didn’t win the gong. The Palm went to the overvalued The Tree of Life (pop pantheism for the unthinking classes) from US director Terrence Malick. But they did win the runner-up Grand Jury Prize. Prior to that, their film festival record has included two Golden Palms, for Rosetta (1999) and L’Enfant (2005), and a sprinkling of other honours.

The Kid, which has speedily circulated to world arthouses and now at long last has a March UK release date confirmed, is a Dardenne first on two counts. It has a well-known actress in a leading role, Cécile de France (of Clint Eastwood’s Hereafter) as the caring hairdresser who becomes a kind of substitute mother – “we wanted to see if we could make space for a star in our territory and whether she would enrich it” – and it has music. Most Dardenne films use only the plainchant of human dialogue; this one provides moments of transcendent beauty with a single Beethoven phrase, gorgeous and benedictive, recurringly used in scenes with the boy.

“It’s a grace, a caress, a moment of gentleness,” says Jean-Pierre, the 60-year-old elder brother with whiter, thicker hair, who leans closer to the tape recorder than Luc (57, ascetic-looking, his pate monkishly tonsured by nature). “It’s the consolation for a boy who’s been isolated and lonely. The phrase we chose, from the adagio of Beethoven’s fifth piano concerto, seemed exactly what we wanted to express.”

The idea for the film came from a true story. Typically for the Dardennes, it was the tale of a socially and emotionally deprived youngster awaiting one of those everyday miracles – moments of grace – that can transfigure a life. “We met, by chance, a woman judge who dealt with youth cases. One of the boys in her care had been placed in an orphanage by his father, who promised to get back in touch but never did. The boy spent years waiting for him. We became obsessed with this story but for years were never able to work out how to do it. From time to time we felt that the boy was walking to our office, knocking on the door and saying, ‘Well, where’s my film?’ ”

The Dardennes are fascinated by children. In film after film, whether troubled teens (Rosetta), tug-of-war tots (L’Enfant) or surrogate sons (Le Fils), they catalyse the plot and shape its conundrums. As inadvertent saviours, they bring crisis and the possibility of redemption. (But I get a very strong “No” when I ask if their new film is a religious allegory.)

The child in The Kid with a Bike is played with charm and huge conviction by Thomas Doret: a ruddy-faced, snub-nosed impetuous youngster with eyes that feed on each passing detail in his everyday life.

“Many directors have said that you can’t direct a child,” says Jean-Pierre. “But we worked with Thomas, and the other actors, for two months. It’s a delicate balancing act. If you direct or instruct him too much, he’s a child doing what an adult is telling him to do.”

Luc: “We rehearse that long because we want everything to be simple when we go on set. The actors must rid themselves of any sense of performance.”

Jean-Pierre: “We rehearse with a small video camera, so they can be free to do and move as they wish while helping us determine what the camera’s movements will be when we shoot. We never say to an actor, ‘Stand here, or stand there.’ It must come from themselves, from their own rhythms.”