Also, studies have generally hinted that the causation here goes the other way: if you have kids, you are likelier to become a loony hard-right evangelical. You don't necessary start out that way.
So what is it about having kids that causes people's brains to melt?
Which is why myself and other parents have become increasingly more liberal since the birth of our kids. Republicans are downright risky for the future.
Furthermore, let's take these poles with a grain of salt considering they are being made at a time when Democratic popularity is in a really fast one. Families with children have always tended to be more Republican. You're talking about people that tend to be older than none child in the household families, more economically established, more religious and conservative in general, etc etc