It’s a brilliantly sunny, bitingly cold day in the glens of Antrim. Beside the little marina at Glenarm, frost is still lying on the spire of the parish church and on the nearby castle’s turrets and battlements. The sea may be sapphire blue, but the white-topped waves pounding on the sand have a distinctly arctic look.

This pretty coastal village is normally a sleepy spot, particularly on a midweek winter morning. But for the past week the harbourside car park has been full of trucks, vans, Portakabins and people carriers.

A group of children come into view, walking along the long stone jetty. Their leader is a dark-haired girl in a red duffel coat; beside her is a tiny chap in a Davy Crockett hat. These are not local kids but a group of young actors. The paraphernalia and personnel surrounding them are part of a feature film being shot on one of the most beautiful stretches of coast in the country.

A Christmas Star is the first family Christmas film to be made in Ireland. Appropriately, its provenance is neither a big commercial film studio nor an ambitious small independent but the Belfast-based Cinemagic International Film and Television Festival for Young People, which uses film and all forms of moving image to entertain, educate, motivate and inspire young people. Established in 1989, Cinemagic is the largest film event of its kind in Ireland and Britain, attracting more than 35,000 young people annually. Seven years ago it was set up in Dublin; five years ago in New York, Boston, Los Angeles and San Francisco. Last year was its first time in London, and there is now a Cinemagic festival in Castres, in southern France. Next November's world premiere of A Christmas Star will bring to a close its 25th-birthday celebrations.

But, with less than perfect timing, just days after the film wrapped, BBC Northern Ireland was reporting that some of the region’s best-known film organisations were facing funding cuts of up to 50 per cent.

Reflecting on this bombshell is Cinemagic's chief executive, Joan Burney Keatings, the producer and driving force behind this project.

“The impact of the proposed 50 per cent funding cuts will be far reaching, with a minimum of 20,000 young people being affected,” she says. “Cinemagic would have to dramatically reduce the scope and scale of its work. The proposed funding cuts will threaten Cinemagic’s role in enabling young people to engage with and experience film and film culture, as well as providing specific opportunities for those wishing to learn about or forge a career in the film and television industry.”

A Christmas Star was conceived as much more than just a movie. Thousands auditioned earlier in the year. The young cast and trainee crew members have been mentored throughout the production process by a team of industry professionals, including a number of Oscar and Bafta winners. Among the well-known names in the cast are Rob James-Collier of Downton Abbey, Suranne Jones of Scott & Bailey, Bronagh Waugh of The Fall and the comedian Kevin McAleer.

Having programmed all manner of age-appropriate screenings in her 13-year tenure, Burney Keatings was struck by the thought that just maybe the time was ripe for the organisation to take a deep breath and make its own movie.

“We’d made a number of very successful short films, and I thought, Why not take it to the next stage?” she says. “It’s all happened very quickly. The idea came to me only a year ago, but in that time we have had so much support from so many quarters. Yes, there have been difficult days, but you have to believe in your vision, take the knocks and never lose sight of the bigger picture. I felt strongly that this could be a transformational project for a lot of people, and nothing was going to put me off.

“The film has brought together young people from different cultural backgrounds from all over Ireland. They will finish the project with a wealth of skills, experience and, most importantly, their first credit on a feature film.”

Maire Campbell, the film's writer, has set her screenplay in the village of Potter's Glen, from where the central character, Pat, left under a cloud, many years previously. He has returned from across the Atlantic a wealthy man, with a teenage son in tow. He pledges to breathe new life into the village, but secretly his plan is to demolish many of the picturesque buildings and build a casino. While the optimistic adults fall for his sweet talk, a group of local children are on to his deception and take radical steps to thwart his actions.

First on-screen credits

Rob James-Collier, who was born in Salford, in England, is perfectly cast as Pat, given his more familiar on-screen persona as Thomas, the treacherous footman in

Downton Abbey

. In real life he is self-effacing, with a dry sense of humour. He came to acting via an unconventional route and says that he knows better than most how precious that first screen credit is. “I have a degree in business studies and marketing, but I knew pretty soon after graduating that I’d made a mistake,” he says. “I really didn’t want to do a real job. I looked in the Yellow Pages and found an acting school in Manchester offering two-hour courses for £20 a throw.

“I’m testament to the fact that you don’t need a drama-school training to be an actor. There’s so much guerilla-style casting now, with kids from estates being recruited and turning in real, raw performances. It’s great that the kids in this film are getting their first on-screen credits. It’s a super profile for them.”

His own first break was in the BBC series Down to Earth, which he says was a big learning curve. Then came Downton and the challenging role that has put him on a whole new footing. "It has been brilliant to develop Thomas," he says. "He's one of the more complex characters, struggling with his sexuality at a time when being gay was against the law. Julian" – Lord Fellowes, Downton Abbey's creator, who is also Cinemagic's patron – "has invested a lot in him. It's amazing to be a part of such a worldwide success story.

“My mum is from Donegal, and we used to come through the North every summer on our way there for holidays. I remember soldiers in the streets and checkpoints along the roads. Now Belfast is unrecognisable.”

Spectacular final scene

A feeling of family and fellowship has developed among the young core cast and their parents, some of whom have visited the locations – including the senate chamber at Stormont – for the first time. The spectacular final scene of the movie was the first to be shot, in front of 12,500 people at the switching on of the Christmas lights outside Belfast City Hall.

"It was unforgettable," says Anne Haughey, mother of 11-year-old Alecoe Haughey, from Co Donegal. "I mean, Alecoe comes from Killybegs. When would she ever have the opportunity to be part of such an event? These children have been chosen from over 5,000 others. As the recalls started to come through, it became very nerve-racking."

John Moan, who was born in Iowa, never dreamed that, with his American accent, he would stand a chance. But the role of Pat's son Junior, who was raised in the US, could have been written for him. Seán Ronan from Dublin, who has appeared in Fair City on RTÉ, as well as in several short films, hopes to emulate the screen success of his cousin Saoirse Ronan. Patrick Roe from Newry says he feels happiest when he is acting and is in a little world of his own. And the biggest personality of them all is in the smallest body on set. James Stockdale may be only three feet tall, but already he has impressed the casting guru John Hubbard, who awarded him the most-promising-actor prize in last year's Cinemagic acting masterclass.

“It has all gelled together amazingly well and has given so many young people the confidence and self-belief to achieve things which, in the past, they may have drawn back from,” says Burney Keatings.

“The spirit of friendship that has prevailed has been truly heart-warming. The young people have felt safe with each other and have worked so well together in an environment which encourages mutual support. The level of involvement has been incredible. Together with the core cast and the trainee crew members we brought in 50 young extras as well as the huge crowd outside Belfast City Hall. In all that makes a total of around 14,000, with everyone playing their part in a project which has captured the hearts of so many people.”

The world premiere of A Christmas Star will be on November 4th, 2015, in Belfast. It will also be will be broadcast by BBC and UTV over Christmas 2015