In a sweaty Portakabin in Edinburgh, a standup makes his entrance to Let It Go from Frozen. He is dressed as a chicken, complete with feather boa and yellow tights, and before long is clucking among the audience, dancing and laying eggs. This, explains standup Owen Roberts, is what happens when you let a six-year-old girl create your fringe comedy show.

The idea came to Roberts, who usually performs with the sketch trio Beasts, when he was trying to write his first solo material. After spending the day in front of a blank computer screen, he went to pick up his partner’s garrulous daughter, Isabella, from school. Isabella, he realised, was full of imagination and energy. Could she rescue him in this moment of desperation? After all, he helps her with her homework.

Once he had suggested it, Isabella ran with the idea of creating a play that Roberts could stage for her. He realised that the best way to collaborate would be to make audio recordings of their brainstorming sessions. This was partly because he couldn’t keep up with her “free-form verbal diarrhoea” and partly because, as a six-year-old, it takes her too long to write down her ideas herself. “I’ve got hours of recordings of her just saying whatever came into her head,” he says. “You can do a writing session for half an hour and then her attention has gone. It burns bright and short. You need to catch that burst of enthusiasm.”

Roberts with Isabella, who wants to be an explorer or hairdresser when she grows up.

In Beasts’ sketches, Roberts’ persona is usually that of “the put-upon person in the group – the other two guys are always trying to sabotage the show”. While working with Isabella, he realised that she too could play the role of antagonist. He relates his exasperation at keeping up with the ideas and demands of his new writing partner, who is soon demanding 50% of the ticket sales. In the show, he describes her outlandish ideas for what should happen on stage, and we see her drawings and hear her outlining plots about aliens, asteroids and clumsy police officers. He then calls up the audience to help him bring these ideas to life on a fringe budget.

Along the way, there are plenty of jokes about aspects of domestic life, including battling to get your children to brush their teeth and what happens when the tooth fairy forgets to visit. The show also explores social perceptions of family life. Roberts met Isabella after he had been going out with her mother for a couple of months and, two years later, they all live together. He takes Isabella to school, makes her meals, comforts her: they share their lives with each other. There is an awkwardness to the description of her as “his girlfriend’s daughter” that belies their close relationship.

Isabella is excited about seeing the show later in the month, when Roberts will be staging a less sweary, more child-friendly version. “I think she imagines it is going to be performed in a big West End theatre, like Matilda,” he says. “She’ll have a rude awakening when she sees it’s in a Portakabin.”

In the show, the audio clips of Isabella – who wants to be an explorer or a hairdresser when she grows up, and whose many nicknames include Snizzelly – get the sort of laughs that most standups at Edinburgh would die for. Collaborating with her, says Roberts, has been liberating because “she’s got no filter”. Her confidence, too, has been inspiring for the 34-year-old comic, who explains that he tends to shut down a lot of his own ideas before they properly take shape. “Everything she says, she thinks is absolute genius. She has absolute faith in everything she does.” And the show’s ending, invented by Snizzelly and excruciatingly performed by Roberts, may be one of the funniest and most surreal things at this year’s fringe.

