"An implicit assumption about the efficacy of government policy in changing family structure also undergirds many proposals by liberals. Concerned with the alarming rate of poverty among children, especially those in single-parent families, liberals advocate actions such as subsidizing child care, providing medical care to working poor families, mandating maternal and paternal leave, and instituting children's allowances. They argue that these measures would strengthen and support two-parent families and lessen the pressures and stresses that lead to the formation of poor single parent families.
Before heeding either the conservatives' calls for a reduced role in family issues or the liberals' calls for a more supportive government role, policymakers need a better understanding of what the impact of government policies has been."
-- "The Links Between Government Policy and Family Structure: What Matters and What Doesn't", M. J. Bane and P. A. Jargowsky, 219-220, chapter 6 of "The Changing American Family and Public Policy", edicated by A. J. Cherlin, COPYRIGHT 1988
So, yeah, no, liberals have not just only recently noticed the connection between single-family households and endemic poverty.