This registration consists of a list of research questions and predictions for the collaborative project, “The Evolutionary Dynamics of Religion, Family Size, and Child Success,” funded by the Templeton Foundation (https://www.evolutionarydemographyofreligion.org). More information about the project is available on its OSF page: https://osf.io/b865v/. The primary objective of this project is to provide novel cross-cultural data to study the relationship between religion, family size, cooperation, and women and children’s wellbeing. Using newly collected demographic, ethnographic and physiological data from five countries - Bangladesh, the Gambia, India, Malawi, and the United States - we aim to answer ten research questions (RQs) and make a number of specific predictions for each. We also include a list of key indicators, a brief outline of the study design, and a data analysis plan. As this project involves a complex multi-site qualitative and quantitative data collection process, we anticipate that these documents may be updated after data collection is complete due to potential constraints during data collection.