>> Coltrane has found that after controlling for variables like age and education, married American men earn significantly more than their unmarried or divorced male peers, and their earnings go up with every child they have. Marriage seems to make men more productive at work because it allows them to outsource much of the housekeeping to their wives.<<

I don't see how that last sentence makes any sense. Since when does one's earnings have anything to do with whether the housekeeping for one child or three children is "outsourced" to wives? I think it's far more likely that being a father to more children is correlated with being older and more experienced and therefore more highly compensated.