What is the theme in If the Witness Lied by Caroline B. Cooney?

One of the primary themes that run throughout the novel is growing up and coming of age, even against adversity such as losing both parents to death. Jack struggles with the fact that his coming of age includes having to grow up faster than his peers because he has become the primary caretaker of his youngest brother, Tris, in the absence of their parents. All of the Fountain children, except Tris who is too young to understand, have to face adult problems, such as death, when they still children.