Research in child development reveals that the sources, level, stability, and uses of family resources have a profound effect on children's well-being and long-term outcomes. Although that research has incorporated economic constructs and measures, developmentalists generally ignore the formal economic framework for thinking about family resources and child outcomes. Building on the premise that children are an investment, that framework explains how families allocate resources and links that decision to other family choices and to key child outcomes, such as schooling, morbidity, and mortality among others. This article explains economists' general approach to family behavior (the so-called theory of household production) and then describes how that framework is useful for thinking about families and children. The article then outlines how economists model parental investment in children and examines the implications of that approach for developmental science. This discussion is illustrated using an example of interest to developmentalists--the involvement of children and adolescents in after-school activities. A concluding section discusses the benefits of and potential barriers to collaboration between economists and developmentalists.