Millions of Americans have weathered the COVID-19 pandemic with the help of direct cash payments from the U.S. government, via stimulus checks, extra unemployment benefits and the expanded Child Tax Credit. But that last financial buffer may come to an end on December 15 when the IRS sends out the sixth — and potentially last — check to parents. That would close the door on the nation's biggest federal cash-assistance programs, which began in 2020. Experts credit those six months of direct payments with helping millions of low- and middle-income families afford basics like food, rent and car repairs, as...