Following the material turn in the humanities, this book brings perspectives from science and ecology into dialogue with children's fiction written and published in the UK and the USA in the 21st century. It develops the concept of entanglement, which originated in 20th-century quantum physics but has been applied to cultural critique, through a reading of Fantastika literature. Surveying a wide-ranging scope of literary texts, this book covers the gothic, fantasy, the Weird, and other forms of speculative fiction to argue that Fantastika positions entanglement as an ethical imperative that transforms our imaginative relationship with materiality. In so doing, it synthesizes perspectives from a similarly diverse range of areas, including ecology, physics, anthropology, and literary studies, to examine the storied matter of children's Fantastika as ground from which we might begin to imagine an as-yet-unrealised future that addresses the problems of our present.