Starting from the early 2000s, the European Union (EU) has increasingly portrayed itself as a global champion for children’s rights. At the same time, in its initial agenda setting, the organisation focused mainly on children’s rights outside the EU. Only recently, it fully committed itself to ensuring children’s rights within the union, for instance, with the adoption of the European Child Guarantee in 2021. What explains this shift? Combining process-tracing with semi-structured interviews with officials in the EU, the Council of Europe as well as NGOs and UN agencies surrounding them, this paper argues that the EU’s policy change on children’s rights can be explained through a combination of bureaucratic agency and member state self-legitimation. EU bureaucrats leveraged member state representatives’ self-legitimation narratives of the EU as a children’s rights champion to expand children’s rights standards not only in its external but also internal dimension. Member states’ need for a coherent organisational self and a sense of moral authority thus became a tool for bureaucrats to exercise agency and push for policy change. The paper underscores the need for further research into how issue adoption can serve as a self-legitimizing practice and concludes that coherence of issue adoption is a significant and underexplored aspect of IO self-legitimation.