Children's literature is increasingly being realized in app format, with its possibilities of combining text, music, sound effects, stills, animated movies, verbal language and, not least, interactivity. This digital and medial literary development calls for new analytical approaches to explore its manifestation in children's literature--its materiality in particular. Exploring and analyzing the app "Sofus and the Moonmachine" by Burup et al. (Sofus and the Moonmaschine, The Outer Zone, Copenhagen, 2016), which integrates various art forms and sensory appeals and prompts different reading paths and types of interaction, this article suggests how a materiality approach can shed light on the formation of meaning in literary apps for children. The analysis is founded on three aspects of the materiality of literary apps: its manifestation as text, its embedment in a medium, and its manner of being and interacting with the world. The scholar of literature and technology, N. Katherine Hayles, has particularly emphasized the materiality of literature, and her theoretical framework will be combined with cultural theory on materiality and theory in children's literature in order to examine how the concept of materiality may be used in approaching an understanding of literary apps for children and cross-media reading.