The United Nations Sustainable Development Goals for 2015-2030 strive for a world that is "just, equitable, and inclusive," in which everyone receives care, education, and opportunities to thrive. Yet many children are living on the margins of society, face multiple disadvantages, and are excluded from full participation in all that life has to offer. To examine the science, economics, and politics of investing in the health, education, nutrition, and social protection of children at the margins, the National Academies of Sciences, Engineering, and Medicine held a workshop in Prague, Czech Republic in November 2015. Held in partnership with the Open Society Foundations and the International Step by Step Association, the workshop convened a diverse group of stakeholders from around the world for 2 days of discussion. This report summarizes the presentations and discussions from the workshop.