This book considers that contextual factors are important for the achievement of social justice and it recognizes that vulnerability to which children are exposed is a phenomenon throughout the planet, particularly in the South. It presents a theoretical review of social justice as well as different situations of vulnerability children experience in their daily lives in which they can be injured, affecting their well-being and the exercise of their rights. It examines the impact of the COVID-19 pandemic on children, considered as a vulnerable group warranting special social policy considerations. It also presents the need to change power structures in knowledge production and decision-making processes to achieve social justice for children; the importance of investing in children; the exclusion of children from participation in certain activities and the shame of not being able to participate in equal conditions with others;  the lives of migrant children belonging to ethnic minorities exposed to language barriers and access to technological devices; and the analysis of the process of social re-integration of children from conditions of armed conflict. The book concludes that governments need to assume social justice as part of universal human interests, providing security, conditions for well-being, and guaranteeing social justice for all children.