This article uses the framework of transitional justice to examine two prominent examples of national public inquiries into institutional child abuse: the Irish Commission into Child Abuse of 2000-09 and the Australian Royal Commission into Institutional Responses to Child Sexual Abuse of 2013-2017. It provides a detailed account of the practical workings of each inquiry in the context of the Irish and Australian political and legal environments, with a view to highlighting the particular nation-building function each played in informing a narrative about transitioning from the past to the present. Public inquiries are increasingly used by democratic states as a form of political and legal reckoning for mass crimes committed on children in the care of the state, with inspiration drawn from other examples of the political redress of atrocities (such as war crimes). While transitional justice approaches to peacetime human rights abuses have much to offer in their promise of truth recovery and accountability, they are limited in their ability to achieve justice in the context of consolidated democracies where the 'transition' from the past to the present is ambiguous and incomplete. This article points to the benefits of the national public inquiry approach to addressing institutional child abuse, while offering cautions about the expectations of transitional justice in this context, through the landmark examples of Ireland and Australia.