This report from the Center on the Developing Child at Harvard University discusses how child welfare systems can use developmental science to better support the children, families, and communities that they serve. The Center intended this report for leaders of public child welfare agencies; private, nonprofit organizations; juvenile and family courts; and legislative committees that work on public policy related to child welfare. The first part of this report focuses on child development and how adversity, such as toxic stress, can disrupt healthy development. The second part outlines how developmental science can improve outcomes in three ways: reduce external sources of stress, develop responsive relationships, and strengthen core life skills. (author abstract modified)