As underdog tales go, it takes some beating. A first-year film student in his early twenties set out to make a documentary in a South African orphanage for children who have lost their parents to Aids. He had a skeleton crew, shooting the film himself and roping in a floating group of helpers. Initially, it was funded with just £10,000 and some credit-card debts.

We Are Together went on to win prizes at film festivals all over the world, including the audience prize and a special jury award at the eminent Tribeca Film Festival and the audience prize at Edinburgh, where it beat the Pixar animation Ratatouille.

But having pledged that all the profits from the film would be donated to the orphanage, the director Paul Taylor is still trying to pay off his debts and, in the meantime, is living with his mum just outside Birmingham.

“We've been very lucky,” says the self-effacing Taylor, now 25, who admits that on paper the movie could sound like a bit of a tough sell. “A film about South African Aids orphans: you think it's going to be a depressing film or a worthy film or a film I should see maybe but it's not going to be an enjoyable, uplifting film.” Word of mouth, he says, has been invaluable in persuading audiences into the cinema.

It's not hard to fathom why the film has been such a success - the spirit and optimism of the movie, or specifically its subjects, is as infectious and inspiring as the songs the children sing together in their daily choir practice. The choir is central, both to the film and to life at this chronically underfunded orphanage. It provides a valuable structure and routine for the children and a means to connect with the world outside. At the outset of the film, the choir is preparing for a trip to Britain. “What do we know about England?” asks one of the care workers. “I heard there are no monkeys,” one child says. “They say we will be getting nice food on the aeroplane,” beams another.

Of all the children, it is 12-year-old Slindile Moya who soon claims the central role in the film. One of the choir's lead singers, she has a gorgeous raw voice bruised by a sadness beyond her years, and she takes a shy pleasure in confiding to the camera. Her family is divided: her two older sisters and her older brother still live in a family home that overlooks the graves of her parents. But financial pressures mean that Slindile, her younger sister and her scene-stealing little brother all live at the Agape orphanage.

Visits home are emotionally charged. The family are incredibly close - the title of the film comes from a song they sing together, beautifully, for the camera. But the shadow of HIV has not yet left the household - Slindile's older brother, Sifiso, is sick. As the film progresses, his health deteriorates and the inevitable diagnosis is made. Even the most intimate moments of grief for the Moya family are shared with Taylor. The camera is treated like a trusted friend.

This intimacy is the result of Taylor's dedication. When the idea for the film came to him, he had already spent three months working at the orphanage as a volunteer. One of the motivations for going back to make the film, he says, was simply to see the children again because he was missing them.

The film-making took place over three years and was plagued by uncertainty. The original choir trip to Britain was cancelled when funding fell through, leaving Taylor without an ending for his film. Then, when he had returned home, a fire destroyed the orphanage. “We weren't there for the fire, and we couldn't afford to go back. We were really upset for the kids, sad we couldn't be there.”

Fortunately, the indomitable spirit that the film set out to celebrate in the first place ultimately triumphed. The choir got to take their music to a charity concert in New York and Taylor got an ending for his film. But with 180 hours of raw footage, and no money left, Taylor and his producer, Teddy Leifer, hit another wall.

It was then that Channel 4's British Documentary Film Foundation, run by the doyenne of documentary, Jess Search, stepped in to save the day. “The sample footage we saw was very powerful,” she says. “When a small amount of material can induce those kinds of strong reactions, you know it's something good. We were, frankly, shocked by how young they were. Their material was so accomplished we were expecting a much older team.”

Galvanised by the experience of being able to use the film to help its subjects - money raised has funded the children's education - Taylor and Leifer have started a company called Rise Films. “Its goal is to use films to help to generate funds for projects in the developing world.” Their first production is the latest film by the documentary-maker Kim Longinotto, also set in South Africa. Taylor, meanwhile is looking for his next directing project, but concedes that it's probably time he earned a bit of money.

We Are Together is on limited release from tomorrow. The soundtrack is on EMI. For details and to donate, please visit www.wearetogether.org.

Food for thought — the top documentaries of 2008

Terror's Advocate

Barbet Schroeder's controversial film about Jacques Vergès, the lawyer notorious for defending terrorists and Nazi war criminals such as Klaus Barbie, refuses to take a moral stance regarding its divisive central character. The result is a thorough, thought- provoking but somewhat uncomfortable character study that invites the audience to make up their own minds.

Release: May 16

Man on Wire

It was described as “the artistic crime of the century”. In 1974 a young Frenchman, Phillipe Petit, stepped out on to a wire strung between the twin towers of the World Trade Centre. He performed on the tightrope for nearly an hour before being arrested. The British director James Marsh's Sundance prize-winning film explores the preparation for this audacious feat.

Release: TBC

Manufactured Landscapes

Jennifer Baichwal's award-winning film documents the work of the Canadian photographer Edward Burtynsky, who finds an unsettling beauty and a horror in vast industrial vistas: rubbish dumps, dockyards, superfactories, quarries. Like the work of its subject, the film is strikingly handsome. The environmental cost to these ravaged landscapes is the unavoidably ugly flipside.

Release: May 9

Standard Operating Procedure The veteran documentary film-maker Errol Morris returns with a gruelling examination of abuse and torture of suspected terrorists by US forces at the Abu Ghraib prison. He interviews five of the seven military police indicted. The film won the Silver Bear at Berlin.

Release: TBC

Roman Polanski: Wanted and Desired

Marina Zenovich re-examines the case that tarnished Polanski's reputation 30 years ago: his conviction for having unlawful sex with a minor, and his flight from the US. She makes a persuasive case for a miscarriage of justice.

Release: TBC

Explore Film

• Film Reviews

• Trailers

• DVD

• Oscars

• Cannes

Editor's choice

• U2 at Nou Camp Stadium, Barcelona
• The 50 Best Movie Villains
• The 15 golden rules of theatre etiquette