If I were you I would begin by focusing on the initial chapters of this excellent novel and the way in which we see Charlie being bullied and intimidated by his father, Allie Fox, who is clearly the force in the family. In many ways, the novel can be considered to be focused on, amongst other things, the development of Charlie Fox as a character who starts off in the beginning slavishly dependent on his father and does whatever he says, moving to his open rebellion against him. Charlie Fox could therefore be said to be timid at the beginning of the novel when he obeys his father and believes what he says about the US and how it is being destroyed. The way that he unquestioningly follows his father to Honduras shows his meekness. This is something that is continued to be shown through the various initiation rites that Allie Fox forces his son to endure. Charlie, at the beginning of the novel, is never able to challenge his father openly and is used by his father as an agent to control the younger children, who find it difficult to complete the challenging tasks they are given.
His secretive nature is shown in the way that Charlie establishes a separate camp from the family camp, called the Acre, where he and the children are able to briefly escape Allie's totalitarian rule and can live a life that is more playful and fun. Bit by bit, as Charlie is confronted by his father's megalomania and madness more and more, he begins to move to try and take over power from him, again demonstrating his secretive nature.