marriage and the federal tax and transfer system

"Someone looking at our system from Mars would conclude that we don’t want moderate income families with children to marry, since we penalize them, but we do want older households (at ages when children are likely to be gone) to marry, since we subsidize them. "
http://www.urban.org/UploadedPDF/901508-Marginal-Tax-Rates-Work-and-the-Nations-Real-Tax-System.pdf