Modern family life brings with it profound changes to children's family living arrangements. An increasing number of children live with unmarried parents whose informal cohabitation implies unequal rights in terms of access to welfare benefit and social protection programmes compared to those in married life. In addition, children experiencing family dissolution are increasingly likely to share their time between the two homes of the separated parents, and/or to live in a stepfamily. The family living arrangements that result from these trends are very diverse and generally not well identified by official statistics, as well as their consequences on families’ living standards. This paper takes stock of the trends in children's family living arrangements based on available international statistics and calls for the development of data that more accurately and reliably reflect children's family situation and its economic consequences. It also discusses adaptations of social protection systems to ensure that all children receive support appropriate to their concrete family living arrangements, and to guarantee that children in a non-traditional family setting are treated on an equal footing vis-à-vis children with married parents. The paper particularly discusses issues raised by the fact that children whose parents live together informally do not always have the same legal and economic security as children of married couples. It also reviews challenges associated with the fact that parents are increasingly sharing custody of their children after separation.