Transitioning into an uncertain adulthood For thousands of migrant children and young people in Europe, turning 18 means transitioning into an uncertain future, with too few resources to navigate this phase of their life. Without a secure residence permit, undocumented young people, whether unaccompanied or in families, are prevented from doing most of the things that their peers do, like studying, working, or getting a driver’s license. Unaccompanied children, specifically, lose the protection they had from deportation and must often leave wherever they were living, and risk becoming homeless. Yet too few countries have policies and procedures that prevent children from becoming undocumented adults once they turn 18. Too few provide access to longer term residence permits to children and young people transitioning into adulthood. Even when residence procedures do exist, they can be incredibly hard to access in practice. In a recent report, we review the support undocumented migrant children and young people need and receive, and how governments treat them when they turn 18. In particular, the report provides an overview of how European countries (with a focus on Belgium, Germany, Greece, Spain, Sweden, and the UK) facilitate or hinder access to secure residence status. We call on states to support all children and young people in this vulnerable phase of life and prevent children from ageing out as undocumented adults by developing regularisation mechanisms and identifying a durable solution for all children.