Fewer children in the United States grow up with both biological parents than in any other affluent country for which data are available.
Here is another bit:
Genuine progress probably hinges on poor or less-educated women delaying childbirth. Eventually, this will happen; the teen birthrate has already been dropping for nearly two decades, albeit slowly. For its part, Washington (or any other government) has only limited tools to speed it up.
That is from Lane Kenworthy, from his article on why opportunity has slowed down in the United States, hat tip Brad DeLong.