One of the biggest changes in American society in the last half century has been the explosive increase in the number of children not living with both biological parents. The decline of marriage and the rapid increase in births outside of marriage are overwhelmingly class phenomena. To oversimplify, the rich marry and have small families, both of which help them stay wealthy and pass on their socio-economic position to their children.
Compared to both the upper class today and to all Americans in the mid-20th century, including the poor at that time, poor women today are far less likely to marry. They also have more children than middle class women and are far more likely to have children who are not raised by both parents.
This creates severe handicaps for the next generation, which also perpetuates the class divide. Even the middle class is being caught in this demographic tug of war, as middle class girls who get pregnant and have kids without marriage are increasingly slipping into poverty as a result.