This paper examines families of children who transition from private to public health insurance. These transitions include, but are not limited to, transitions that con-stitute crowd-out. We pool longitudinal panels from the Survey of Income and Program Participation (SIPP) covering 1990 to 2005. The annual rate of children who transition from private to public coverage more than doubled over this period, although it remains small. Transitioning children in recent years are typically in working families with median incomes of around 200% of poverty. Children who transition from private to public coverage are more likely to belong to minority groups, to have lower incomes, and to be in poorer health than children remaining privately insured. Public coverage now provides important protections for low-income working families, especially those with children in poor health. These findings underscore the need to implement post-health-reform policies with an eye towards possible adverse selection into public programs.