John Graunt's pioneering study, Natural and Political Observations Made upon on the Bills of Mortality (1662) has been overlooked as a source for ideas about the importance of child mortality in an urban environment. Graunt seems to have been the first to arrive at an infant mortality rate (IMR), but this has been little explored. Graunt helped to define ‘the urban penalty’, but not in terms of the IMR. The article explains Graunt's focus on other aspects of urban mortality in relation to his need to reassure those in government, his methodology, and above all his gender. For context, the article looks at attitudes to childhood among members of the influential Hartlib circle of reformers, with which Graunt was connected. These male writers were greatly concerned about children, but seem to have shared with Graunt the traditional idea that children under the age of about seven were the responsibility of women.