One would think that in 2008, you could not deny a woman employment because she has children. But, it seems that this isn't the case. A recent study published in the American Journal of Sociology found that women with children are half as likely to be called back after an interview than women without children. (See related story at ABC.com) Many employers believe that women with children are not reliable or not committed to working.
In most states it is not illegal to ask women if they have children. As long as they ask both men and women the same questions, a company has not done anything illegal. However, if a company asks about kids, they are likely going to use that information to decide not to hire a mom. Of course it is difficult to prove that an employer only asks women about having kids. Further, it is difficult to prove that the kids are the reason the company didn't hire someone.
Some suggest maybe the laws need to change. Right now it is illegal to ask about children in 22 states. I haven't been able to find any evidence on whether or not such laws have any effect on actual outcomes for women. Similar laws in other states certainly couldn't hurt, they would at least give women some recourse if they believe they were discriminated against.
However, I believe maternal profiling will end only when real change takes place in the workplace. When companies are able to offer flexible work options that allow moms (and dads) to meet their family obligations and also get their work done, companies will realize that a mom isn't such a bad hire.