In this article thought experiments are uncovered as key stimuli of philosophical potential in children's literature and their presentation and function is examined in a selection of focal texts, including: Lewis Carroll's "Alice's Adventures in Wonderland" (1865) and "Through the Looking-Glass" (1871); "Even the Parrot" by Dorothy Sayers (1944); Nina Bawden's "Carrie's War" (1974); and "A Game of Soldiers" (1985) by Jan Needle. The thought experiment is a device common to science and philosophy and has been recognised as an heuristic tool in literature generally, but here children's literature is drawn into the conversation, revealing that--as a dynamic mechanism of children's narrative--thought experiments have a long-standing and particular role to play in books for young people. This paper connects with a recent turn in children's literature discourse toward the conditions of power in books for young readers; it moves on the debate by demonstrating that the apparatus of thought experimentation places the implied child reader in a position of philosophical responsibility and forward thinking. Presenting thought experiments in different ways, formal properties of the thought experiment--such as conversational mode, double engagement and modal positioning--are identified and shown to open up a philosophical space of subsequence in children's texts.