 Whatever the prospects of a voluntarist account of parenthood, a voluntarist account of familial relations in general is implausible. The duties that siblings have to each other, or that children have to their parents, are not easily understood as voluntary undertakings. This is a problem for voluntarist accounts of parenthood to the extent that duties between parents and children should fit within a wider framework of familial duties (Rachels 1989; Mills 2003; see Mullin 2010, for discussion; and the entry on  special obligations).