A paper that just came out in Current Biology suggests that children in nonreligious households are more altruistic and are less likely to judge wrongdoers harshly.
Summary: Prosocial behaviors are ubiquitous across societies. They emerge early in ontogeny [ 1 ] and are shaped by interactions between genes and culture [ 2, 3 ]. Over the course of middle childhood, sharing approaches equality in distribution [ 4 ]. Since 5.8 billion humans, representing 84% of the worldwide population, identify as religious [ 5 ], religion is arguably one prevalent facet of culture that influences the development and expression of prosociality. While it is generally accepted that religion contours people’s moral judgments and prosocial behavior, the relation between religiosity and morality is a contentious one. Here, we assessed altruism and third-party evaluation of scenarios depicting interpersonal harm in 1,170 children aged between 5 and 12 years in six countries (Canada, China, Jordan, Turkey, USA, and South Africa), the religiousness of their household, and parent-reported child empathy and sensitivity to justice. Across all countries, parents in religious households reported that their children expressed more empathy and sensitivity for justice in everyday life than non-religious parents. However, religiousness was inversely predictive of children’s altruism and positively correlated with their punitive tendencies. Together these results reveal the similarity across countries in how religion negatively influences children’s altruism, challenging the view that religiosity facilitates prosocial behavior.
Looking at the paper's methodology, it isn't very convincing. There doesn't seem to be any attempt to factor out the effect of region as a moderator variable.