"In Pennsylvania, Marriage Drops the Probability of Child Poverty by 87 Percent," according to just one of a set of 51 state-level reports comparing poverty rates in married and unmarried families. (They can be accessed via the page for Pennsylvania or any other state, though I don't see a link for the whole set).
This is part of a new report by the Heritage Foundation's Robert Rector, titled "Marriage: America’s Greatest Weapon Against Child Poverty".