The right of children to be registered at birth was not part of early universal declarations of entitlements for the young adopted in the wake of the First World War. But during the interwar years, the main proponents of these declarations — the Save the Children International Union and the American Child Health Association, headed by philanthropist and future President Herbert Hoover — soon understood that the registration of infants was at the basis of their work, especially that concerned with the reduction of infant mortality. This chapter studies their respective campaigns in Africa and in the United States, respectively, to show how registration came to be understood as a prerequisite for the full promises of children's rights to be realized. It draws surprising parallels between the two efforts, related to the size of the territory and the discrimination faced by children due to their race and their ethnic origins.