Cool hand Lukas

Lukas Moodysson is hot. Hot, and a bit bothered: London isn't supposed to be this way. He's been in Metrodome's boardroom hard at the PR jaw-jaw all day, but it's the photo shoot in Hyde Park that's put him in a bad mood. "It's harder than talking," he grumbles, ever so slightly crossly.

Still, I know, because I've seen and loved his new film Together, that he's bound to be a sweetie; a cantankerous person simply could not have written a script so full of hope, so ripe with good-heartedness.

I smile, and he looks back at me, resigned to his fate.

Together is Moodysson's follow up to his début feature Fucking Amal (released abroad as Show Me Love in order to protect the more delicate sensibilities of the English-speaking world). Set in a commune in Sweden in the 1970s, it follows the daily conflicts and dramas of human failings and interactions with warm humour and unforced poignancy. Its message is simple: everyone is basically good, and the support of friends, family and community can help them turn their life around. Or, put in the film's own words: "Better to eat porridge together than cutlets alone."

Oh, and everyone should play football, as long as they cheer for the other side's goals as well as their own.

It's a film that leaves you walking high on its optimistic spirit, smiling at the possibilities of life. And, according to Moodysson, it's a film that probably wouldn't have been made if he wasn't a father.

"I think having children makes you much more intelligent," he says. "You learn to see, or at least you try to see, the world from another human being's eyes, and that's extremely important."

After his first child was born, he tells me, his whole attitude to the world and his place in it changed: "Time that you spend away from your children should either be extremely necessary or it should be extremely important."

I think he's paused, but the silence stretches, and then, as I open my mouth to move us along, he finds the words for his thoughts: "For me," he begins again in a voice stripped of emotion by the effort of translation, "I can't do bad things any longer, and without children I could have written some really bad things."

I interrupt to clarify whether he means bad as in poor or dark.

"No, just bad," he shrugs. "I judge myself much harder now. I'm always asking, 'Is this something I should write? Is it something that I should put my time into? Or is it just something I make for fun?' "

"Without children, I don't know, I probably would have made commercials or music videos – or I could have been a writer on a TV series." He stops, frowns, then adds, with a flicker of a sardonic smile: "No, maybe not something as bad as that."

"But," he sighs, "as a father I can only make important things."

He says this with such solemnity I am conscious of quelling my instinct to laugh; Moodysson is young – 32 – and looks even younger; his seriousness fits with the awkwardness of a new suit bought with growing room in mind. But then perhaps he can't help but look vulnerable to me, sitting, as he is, in front of a replica Star Wars Stormtrooper with its gun pointed directly at the back of his head.

Trying to avoid drawing any parallels between this symbolic act of violence going on over his shoulder, and the oh so tricky dynamics of the interview process, I ask him what inspired his flawed yet wonderfully redeemed characters, and we're instantly back to babies again.

"Hopefully, I'm going to leave my children in this world, and they will have to trust all the other people in the world, and if I thought that the world looked like that," he points beyond my head, where an enormous cardboard cutout of Eric Bana as Chopper, a gun in each hand, looms, "then it would be really difficult to leave them here. I'm really fighting for some kind of hope. I believe that everybody, even him" (he gestures towards Bana again) "can change. That's the difference between me and George Bush, because he kills people; he executes them because he doesn't think there's any way they can change."

References to America pepper Moodysson's conversation; it both repels and fascinates him. Having made two films that have outgrossed Hollywood blockbusters on his home turf, he has inevitably had the call enticing him Stateside: "I won't move to LA," he says emphatically. "But I think I will make a film in America. I find it interesting as a cultural phenomenon." Whether America knows what it's letting itself in for is another matter: "I would like to make a film about George Bush," he says, entirely in earnest, "and I have an idea for a film about the American health insurance system."

He's only been in London a couple of days, but he's already horrified by our own cultural obsessions: "It's very disturbing coming here and hearing about the whole James Bulger affair," he frowns. "The hatred against those kids is quite difficult to understand from a Swedish viewpoint. I don't know how people can hate children or see them as evil, and it's quite frightening that that kind of hatred exists in a democracy."

It couldn't have happened in Sweden, he says: "There's no way they would have gone to prison, that would have been unthinkable; in fact there was a very similar case in Norway, and the children continued to go to the same school – I remember seeing an extraordinary interview with the murdered child's mother and she was not looking for revenge at all, she was just feeling extremely sorry for those children who had done this terrible thing."

Though Fucking Amal did, and Together is bound to, break across those cultural boundaries, Moodysson says they were made with only a Swedish audience in mind. Though he describes both films as intrinsically "very Swedish", he recognises the influence of American cinema on his style: "I tried to find those simple, straightforward communicative methods of film-making which many Europeans have avoided for fear of being too simple."

Was he surprised then, that Ingmar Bergman described Fucking Amal as "a young master's first masterpiece"?

"It doesn't surprise you when it happens because you're just so happy that people like the film," he answers blankly.

"But I do have some kind of manic depressive self-confidence," he continues, in a rush. "Sometimes I really feel like it's the emperor's new clothes, that my films are really nothing. They're worthless and I'm stupid and my thoughts are unintelligent and that nothing that comes from my pen is new. But in order to create you have to believe in yourself, even if it makes you psycho in the head."

He stops abruptly, stares at the ceiling a bit, then, looking at his hands, adds: "Sometimes I can only seriously compare myself to Johann Sebastian Bach and, maybe, Bob Dylan."

By the time he meets my astounded gaze, his whole head is burning red with embarrassment, and – it's the moment I've been waiting for – the little boy hiding behind the grown-up success story finally descends into hysterical, naughty giggles.

'Together' is released 13 July and will open the Cambridge Film Festival on 12 July