Abstract: Two national household surveys, the Demographic and Health Surveys and the Multiple Indicator ClusterSurveys, drive assessment of the Millennium DevelopmentGoals, Poverty Reduction Strategies, and other major international platforms in most low- and middle-income countries. However, little attention has been given to the fact that household surveys are limited to people living in households, therefore excluding some of the world’s most vulnerable populations and including the homeless, people living in institutions, and migrant laborers. The situation of children living outside of households is particularly precarious because many of these children are also outside of families or in families that cannot adequately care for them. Deprivation and stress related to these early life experiences can negatively affect health and productivity across the life course. This manuscript reviews the issues facing children outside of households and argues for the importance of gathering robust data about this population to formulate responsive policies and services, mobilize resources, and foster accountability. Cambodia is highlighted to illustrate the recent work that the government has undertaken to quantify two key subgroups of children outside of households: children living in residential care institutions and homeless children living on the street or in other public places. The methods, ethical considerations, and implications ofCambodia’s enumeration are discussed.