Over the last three quarters of a century, international guidelines and regulations have undergone significant changes in how children are problematised as participants in biomedical research. While early guidelines enacted children as vulnerable subjects with diminished autonomy and in need of special protection, beginning in the early 2000s, international regulatory frameworks defined the paediatric population as vulnerable due to unaddressed public health needs. More recently, ethical recommendations have promoted the active engagement of minors as research partners. In this paper, I adopt a post-structuralist approach to policy analysis to examine deep-seated assumptions and presuppositions underlying the changes in the problematisation of children as biomedical research participants over time. While biomedical research ethics focuses on the autonomy and vulnerability of minors, ethical guidelines are situated in specific sociocultural contexts, shaped, among other things, by contingent public health needs and changing conceptions of the value of research and science for society. In the process, I demonstrate the challenge of moving away from an approach that in taking adults as the model overshadows the complexity of children's lived experiences as well as their personal, cultural, and social lives. The lack of acknowledgement of this complexity makes children vulnerable to epistemic injustice, which is particularly crucial to address in public involvement initiatives.