Everything you need to understand or teach Shade's Children by Garth Nix.
Shade's Children is a science fiction novel that portrays a world that has been taken over by seemingly alien beings, called overlords, who have made all of the adults on the planet disappear. The aliens raise children in order to harvest their body parts. A guerilla team of children—some of Shade's children—overthrow the overlords and restore their society. The novel is fast-paced, suspenseful, and full of action, and addresses some important ideas about identity and the role of children in society.
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Garth Nix