WASHINGTON (AP) — The number of children in America living in poverty jumped dramatically after just one month without the expanded child tax credit payments, according to a new study. Advocates fear the lapse in payments could unravel what they say were landmark achievements in poverty reduction. Columbia University’s Center on Poverty and Social Policy estimates 3.7 million more children were living in poverty by January — a 41% increase from December, when families received their last check. The federal aid started last July but ended after President Joe Biden’s Build Back Better bill stalled in the sharply divided Congress.