Working Families Relief Act of 2018 This bill amends the Internal Revenue Code to limit the temporary (for tax years 2018 through 2025) refundable portion of the child tax credit, with respect to any qualifying child, to the greater of: (1) $1,400, or (2) the excess of the taxpayer's Social Security taxes for the year over the credit allowed under the earned income tax credit. (Under current law, the maximum is $1,400, adjusted for inflation after 2018).