Difference, unconventionality and freakiness rule in UglyDolls, the new animated film from STX Entertainment. While many kids films preach about the need for self-acceptance, they tend to feature perfect, unrealistic animated versions of people that don't look much like their audiences. UglyDolls, in comparison, is a breath of fresh air; a good-hearted, fun kids film about celebrating difference and friendship no matter what you look like.

In the town of Uglyville, we meet a host of colourful characters who, curious about the outside world, decide to venture beyond the safety of their town. On the other side of the mountain that shelters Uglyville, they discover another town, Perfection. There, conventional dolls are trained to be 'perfect' before heading out of the town and into the arms of a child. The UglyDolls are forced to grapple with their identities and figure out what it means to be different in a world surrounded by perfection.

While UglyDolls explores relatively deep and timely issues for a kids movie, the film is also a musical adventure, packed full of catchy tunes by the likes of Kelly Clarkson, Nick Jonas, Janelle Monae, Blake Shelton and Pitbull who also lend their speaking voices to the dolls. Other speaking roles are voiced by a similarly star-studded cast, including Wanda Sykes, Emma Roberts, Gabriel Iglesias, Wang Leeho, Bebe Rexha, CharliXCX and Lizzo.

For director, Kelly Asbury, both the music and the emotions behind the film sparked his interest in getting involved with the production. 'I first met with several executives at STX, who presented UglyDolls to me,' he explains. 'Some development work had been done on the proposed movie. Basically, when I heard the opening song 'It Couldn't Get Better' and saw the very emotionally charged ending, I was hooked.'

UglyDolls is as much a music adventure as it is an animated kids film, and Asbury was keen to use the music to hit both narrative and emotional notes. 'My aim was to make UglyDolls a full-on traditional movie musical, like the ones from the 1940s and 50s,' he explains. 'Fun, light-hearted and emotional, where the characters express themselves through songs. Our songwriters Chris Lennertz and Glenn Slater delivered each song as a narrative guide post to reinforce a given character's point-of-view, all while helping move the story forward.'

For a film so driven by its musical numbers, Asbury knew he had to enlist singers at the top of their game who could also do voice acting. 'Once Pitbull and then Kelly Clarkson were signed, it became apparent that most of our cast needed to be very good musical performers as much as actors,' he says. 'We lucked out in that the individuals we selected could also deliver a nice speaking role as well.'

While UglyDolls, the film, is very much its own thing, UglyDolls, the toys, have existed since 2001. 'It's a true love story,' says Asbury explaining the history behind the toy chain. 'The original creators of the UglyDolls [David Horvath and Sun-Min Kim] did so as a means of keeping in touch during a post-college long-distance relationship. The resultant characters evolved into hand-sewn dolls, which other people wanted. Birth of a toy line!'

With so many animated kids films being sequels or spin-offs, UglyDolls is an increasingly rare example of an original animation. While the toys existed before the film, Asbury wanted to create a new world that felt real and that audiences could invest in. 'For me, it is less about putting my stamp on things and more about trying to create a world that the audience believes in and cares about,' he explains. 'I try for sincerity and I try for the characters to genuinely exist and interact within the rules that created reality. It all must appear as if it is really happening. No winking at the audience.'

Similarly, UglyDolls is sincere in its messages of diversity, acceptance and inclusion, all of which feel particularly timely, what with current debates about social media promoting unrealistic standards of beauty. Asbury wanted audiences – both young and old – to look deeper into what perfection means and why difference should be celebrated. 'This movie is about everyone learning to be more kind to one another; to look past our physical differences and give more of a chance to what's inside us; to learn to look in the mirror and give ourselves a break,' he explains. 'To try looking beyond the physical and see the emotional. We all are more alike than meets the eye.'

Not bad for a kids animated film about some cute plushy toys. And which UglyDoll does Ashbury himself relate most to? 'Gibberish Cat, as probably evidenced by my above answers!'

Edinburgh International Film Festival Family Gala: UglyDolls, Festival Theatre, Edinburgh, Sun 23 Jun.