Parenthood Makes Moms More Liberal, Dads More Conservative?

I'm skeptical:

"Parenthood seems to heighten the political 'gender gap,' with women becoming more liberal and men more conservative when it comes to government spending on social welfare issues," says Dr. Steven Greene, an associate professor of political science at NC State and co-author of the study. Greene and Dr. Laurel Elder of Hartwick College used data on the 2008 presidential election from the American National Election Studies to evaluate the voting behavior of men and women who have children at home. Parents who have grown children were not part of the study.

"Basically, women with children in the home were more liberal on social welfare attitudes, and attitudes about the Iraq War, than women without children at home," Greene says, "which is a very different understanding of the politics of mothers than captured by the 'Security Mom' label popular in much media coverage. But men with kids are more conservative on social welfare issues than men without kids."

I'd like to take a closer look at this study. I speculate that what's actually going on is that marriage is correlated with conservatism (whether or not its causal is a different story) whereas unmarried motherhood is correlated with being liberal. Because most single parents (~ 90%) are mothers, women with children in the home are far more likely to be unmarried than men with children in the home. If it is not controlled for, this 'single mom effect' could show up in the data with the appearance that parenthood makes men more conservative and women more liberal, when if fact something else is going on.