Child vulnerability is the outcome of a range of complex factors that compound over time. Across the OECD, millions of children from diverse backgrounds face daily hardships ranging from poor housing and inadequate diets to maltreatment and unsafe neighbourhoods. Vulnerability locks disadvantaged children into disadvantaged adulthood, putting the brakes on social mobility. Investing in vulnerable children is not only an investment in disadvantaged individuals, families and communities, it is an investment in more resilient societies and inclusive economies. This report analyses the individual and environmental factors that contribute to child vulnerability. It calls on OECD countries to develop and implement cross-cutting well-being strategies that focus on empowering vulnerable families; strengthening children’s emotional and social skills; strengthening child protection; improving children’s health and educational outcomes; and reducing child poverty and material deprivation. Such policies reduce the barriers to healthy child development and well-being and increase opportunities and resources, thereby helping vulnerable children build resilience.