This book explores child vulnerability in various contexts from a cross-country, comparative perspective. It shows how vulnerability in childhood develops within subjects in relationships with other people (other children, parents, specialists, such as teachers, social workers, and judges), how it is created by welfare, health care, education, and justice systems, and is empowered by multiple crises, such as the COVID-19 pandemic, wars and natural disasters. The authors hope to enhance dialogue between childhood studies and children’s rights studies through these discussions. The role of children’s agency and autonomy, including their right to participate in decision-making processes related to their own life, has a special emphasis in this book. Importantly, the book discusses ethical considerations and challenges connected to the participation of vulnerable children in research. It also adds insights into domain-based child vulnerability, particularly through participatory action research with extremely vulnerable children with traumatic pasts in Estonian substitute care and Ukrainian children with refugee status in Estonia. The book thereby provides deep insights into the ways to increase child well-being by decreasing vulnerabilities and building resilience. It combines approaches from psychology, sociology, law, educational sciences, social work, and media studies, and is an important resource for academics as well as practitioners and policy-makers working on children's well-being.