What is the theme in Magyk by Angie Sage?

The importance of family is a driving theme in the story because the two main characters - Jenna and Boy 412 - are shaped by their family affiliations and by the new information each receives about their families. Jenna is raised as the only daughter in a household of six sons. She believes Silas and Sarah are her biological parents though she has wondered why she doesn't resemble her parents or brothers. Jenna learns, rather abruptly, that Silas and Sarah are not her parents and that she's the heir to the throne.