The money you hear about people getting just for filing a tax return, claiming kids, is dependent on having some earned income. The money comes from "refundable" tax credits. That is, you get the money even if you have calculated tax to credit against.
Without earned income, you also cannot claim the earned Income Credit or the "Additional Child Tax Credit" (the refundable portion of the $1000 child tax credit). Both are calculated on your earned income.
A little understood fact about these refundable credits is that they were designed to compensate low income wage earners for the burden of FICA (social security & medicare) taxes. Without earned income, you paid no FICA taxes.
