This paper examines the reasons behind the failure of EU and national policy interventions to protect unaccompanied migrant children's (unaccompanied minors - UAMS) rights during the refugee crisis in Europe. By drawing on policy documents and empirical data, it is argued that the deficient protection of UAMS' child rights was essentially a failure of responsibility allocation in line with the "bystander effect" analytical explanation. While this argument does not disregard the role of other explanatory factors, such as the lack of European solidarity, poor legal enforcement and financial reasons, among others, it is claimed that the diffusion of responsibility (in theory and practice) between various policy systems at the national level, as well as between the EU and domestic levels, contributed to the failure to protect UAMS' child rights across Europe.