Interest in the consequences of family legal status for children has grown in response to immigration-related changes in the ethnic composition of American society. However, few population-based empirical studies devote attention to family legal status because of data limitations. Using restricted data from the California Health Interview Survey (2009), the primary objectives of this research are to identify and evaluate strategies for measuring this important determinant of life chances among Mexican-origin children. The results indicate that measurement strategies matter. Estimates of the size of status-specific segments of this population and their risks of living in poverty are sensitive to how family legal status is operationalized. These findings provide the foundation for a discussion of how various "combinatorial" measurement strategies may rely on untenable assumptions that can be avoided with less reductionist approaches.