From the summary:
Recent proposals in the House and Senate (for example, the Grow American Incomes Now Act) focus on amplifying the Earned Income Tax Credit (EITC)—a refundable tax credit for low-income workers—to compensate for growing wage inequity. We find that the share of EITC filers who are families with children is especially high in the poorest counties (those counties outlined in black on Map 1), including many places throughout the South.
The Earned Income Tax Credit provides tax relief to working people with low to moderate income, with much larger credits for tax filers with children. The credit is refundable, meaning that the EITC reduces the amount of tax owed, and any amount above that may be issued as a refund.