"Shadow Children" refers to a series of novels by author Margaret Peterson Haddix. The books follow the lives of children who are born into a society that enforces strict population control, leading to the existence of illegal "shadow" children who must hide their identities to survive. The main character, Luke Garner, is a third child in a world where families are only allowed two children. As he navigates the dangers of being a shadow child, he discovers others like him and learns about the importance of freedom, identity, and the fight against oppressive societal rules.