This paper develops a new approach to estimating child penalties based on cross-sectional data and pseudo-event studies around child birth. The approach is applied to US data and validated against the state-of-the-art panel data approach. Child penalties can be accurately estimated using cross-sectional data, which are widely available and give more statistical power than typical panel datasets. Five main empirical findings are presented. First, US child penalties have declined significantly over the last five decades, but almost all of this decline occurred during the earlier part of the period. Child penalties have been virtually constant since the 1990s, explaining the slowdown of gender convergence during this period. Second, child penalties vary enormously over space. The employment penalty ranges from 12% in the Dakotas to 38% in Utah, while the earnings penalty ranges from 21% in Vermont to 61% in Utah. Third, child penalties correlate strongly with measures of gender norms. The evolution of child penalties mirrors the evolution of gender progressivity over time, with a greater fall in child penalties in states where gender progressivity has increased more. Fourth, an epidemiological study of gender norms using US-born movers and foreign-born immigrants is presented. The child penalty for US movers is strongly related to the child penalty in their state of birth, adjusting for selection in their state of residence. Parents born in high-penalty states (such as Utah or Idaho) have much larger child penalties than those born in low-penalty states (such as the Dakotas or Rhode Island), conditional on where they live. Similarly, the child penalty for foreign immigrants is strongly related to the child penalty in their country of birth. Immigrants born in high-penalty countries (such as Mexico or Iran) have much larger child penalties than immigrants born in low-penalty countries (such as China or Sweden). Evidence is presented to show that these effects are not driven by selection. Finally, immigrants assimilate to US culture over time: A comparison of child penalties among first-generation and later-generation immigrants shows that differences by country of origin eventually disappear.