I didn't hear this show so I can't be completely sure but they were likely talking about EIC, earned income credit. The limit for a single person is very low but it's easier to fall below the limit if you have kids. The income limit for someone with two or three children goes up above $40K per year.

$43,279 ($48,279 married filing jointly) with three or more qualifying children
$40,295 ($45,295 married filing jointly) with two qualifying children
$35,463 ($40,463 married filing jointly) with one qualifying child
$13,440 ($18,440 married filing jointly) with no qualifying children

The first number is for a single person and the one in parentheses is for married filers.