Saw this in the theater yesterday. It was shot in a 4/3 aspect ratio, not widescreen, which looks strange on a big screen. But that plus the camerawork style was done to lend a cinema-verite look to it.
The lead, Katie Jarvis as Mia, has 100% screen time. Her character is 15 but she was apparently late 16/early 17 when this was filmed, and does an excellent job. She was a neophyte actress, but lived an an area not too much different than that of the film and probably could understand the bleakness of the family's life as the film portrays. And since one theme of the movie is Mia's awkwardness in dealing with growing up and the growing sexual tension with her mom's boyfriend, a new actress seems a good choice. The 11 year old sister, Rebecca Griffiths as Tyler, is more clearly up FLM's alley though probably only 10% screentime. There's a third girl, Sydney Mary Nash (below) as ~6 year old Keira, who only has a few minutes but is worth mentioning.
Not a nice neat story but definitely has its moments, at times very intense, worth seeing.