Background: Little is known about the health literacy of children living with long-term conditions. This study aimed to gain insight into the life of children with a long-term condition in the context of health literacy, specifically their understanding of their health and the barriers and facilitators to sharing information about their condition with others. Design: Child-centred qualitative arts-based approach with children aged 6-12 years. Setting: Children participating in the study came from three countries -- the UK, Australia and New Zealand. Method: A participatory arts-based qualitative child-centred approach prompted children to draw, label and use stickers, body-outlines and collage to describe elements central to health literacy. This encompassed their long-term condition, their understanding of their condition, its management and decision-making associated with sharing information about their condition with others. The sessions were audio-recorded, and reflexive thematic analysis was undertaken. Results: Four central themes related to key elements of child health literacy: (1) pragmatic understanding -- what it feels like and what happens in my body; (2) management regime -- what do I have to do to keep on going; (3) information sharing -- I don't tell random people; and (4) benefits of sharing -- they've got my back. Conclusion: Children indicated a pragmatic or process type understanding of their condition and its management. Children were discerning about who they shared information about their condition with, but tended to establish a network of well-informed peers capable of providing support if needed. Despite gaps in children's health literacy, parents and families have an important role to play in checking children's understandings and developing critical health literacy.