It is well established that unions provide benefits to workers — that they raise wages for their members (and even for nonmembers). They can help reduce inequality. A new study suggests that unions may also help children move up the economic ladder. Researchers at Harvard, Wellesley and the Center for American Progress, a liberal think tank, released a paper Wednesday showing that children born to low-income families typically ascend to higher incomes in metropolitan areas where union membership is higher.