I looked at over 5,000 respondents from the GSS to estimate a model that predict the odds of having at least one child. Here are the results (logistic regression coefficients):
Having at least one child
Years of education -.15
Belief in God .15
Political conservatism .08
All of the relationships are statistically significant at the 95 percent confidence level (two-tailed test). The estimates depend on the scale of the predictor: the income coefficient is so small, for example, because income varies so widely. Income is actually a comparatively strong predictor of not being childless, as is age (not surprisingly). Education is also a strong predictor of having no kids. IQ is weaker. Belief in God is a strong predictor the other way, while conservatism is a weaker predictor.
Long story short: being an educated liberal atheist is like having a disease where your testicles rot and fall off.
And you develop this mysterious desire to get a dog or a cat.