Objective: This paper presents findings of a qualitative study which explored children and young people’s understanding of health and the factors that contribute, or act as barriers, to healthy lifestyles. Views were elicited from consultations with children and young people as part of the process for the development of a National Obesity Policy in Ireland. Design: Child participatory methodology was used which prioritised the voice of the child in policy making. Methods: Two consultations were held – one with 48 children between the ages of 8 and 12 and the other with 34 young people aged 13–17 years. The consultations utilised qualitative participatory methodology which prioritised the voices of children and young people in policy making. A diverse range of methodological tools (e.g. ‘lifelines’, ‘body maps’, world café workshops) were used to collect data and optimise levels of participant engagement. Qualitative visual and written data produced during the consultations was then subjected to thematic analysis. Results: Children and young people’s constructions of health and healthy lifestyles are multifaceted. Participants in the consultation appeared well informed as to the general factors which contribute to healthy and unhealthy lifestyles. There were notable differences of emphasis related to age, with the older age group engaging more with issues relating to mental health and peer relationships, while younger children focused more on balanced diet and exercise. Conclusion: Findings from this consultation suggest that children’s constructions of health, and their understandings of the factors that impact health, are complex and often go beyond medical constructions of the meaning of health. The consultation informed the development of the new National Obesity Policy in a number of ways, including specific actions in relation to the development of a whole school healthy lifestyles programme, developing a health and well-being model for early childhood services, and providing clinical services specifically for children.