Kate Green is the mother of the Green family. She went to spain with Gordon leaving the kids alone. She is twenty-six years old, and had her first child, Lily, when she was 15.
Her role in the book starts when she goes down to the Fox and Hen pub, then goes to a night club and meets Gordon, a 19 year old, and starts a relationship with him. She then goes on holiday to spain with Gordon, leaving the kids all alone. Kate thinks that Mikey is going to look after her children but he never comes.
Near the end she comes back, after it was revealed that Gordon had discovered she was older than he thought, and had kids (he saw their photo in her wallet) and the kids are taken away from her and put into care.
It would seem that due to having kids when she was perhaps too young to really look after them, Kate still mainly acts like a teenager, and lacks responsibilty. She seems to want to try and kid herself that she still is, going out partying and clubbing, as well as allowing Gordon to think she was younger, and didn't tell him she had kids. Deep down, however, she does care for her children, and was upset when they were taken from her.