How did child gender affect deliberations and voting at the 1787 U.S. Constitutional Convention? Though recent scholarship has found profound and far reaching influence of child gender upon the beliefs and behavior of modern parents, there is no reason to believe that this is only an important consideration in the present. Leveraging the natural experiment of child gender, we test whether the gender of a delegate’s children influenced his voting. We hypothesize that fathers of sons would favor creating a strong national government because they could more easily envision their sons holding places in the emergent empire (especially younger sons). Using new data on delegates’ children, we find statistically and substantively significant results: having sons indeed predicts delegates’ favoring a stronger, centralized national government (with daughters showing an opposite effect). These differences are sufficiently large to have likely affected the Convention’s proceedings and therefore the U.S. Constitution.