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Beneath the summer camp fun is a story that is deeply personal for the film's writer and director, George Jaques.

His mother was diagnosed with cancer when he was 15, but it took another eight years for him to feel ready to turn some of those experiences into a script.

"I never seem to write in the moment I'm going through it," Jaques says. "You have to sort of get through and understand it and have that reflection of it."

He stresses that the film is not his family's story, but "there's bits of me" scattered throughout its characters.

Jaques was also conscious his own experience could only take him so far. So, he worked with the Teenage Cancer Trust, hearing from young cancer survivors as well as parents who had lost children.

"I remember going in to do a big talk with some young people who had survived cancer and they were like, 'don't call us kids, do not say we're brave.'"

He says the film was "shaped" by these young people he met - such that he gave two of them roles in it.

Making the movie also forced Jaques to revisit some of his own fears around loss. He recalls a moment during the premiere in Berlin when emotion crept up on him.

"I remember seeing my mother and I realised there's a version of that movie where my mum wasn't sitting in the audience," he says.