The problem is you are comparing apples to oranges. The EITC and Child Care credits are mostly rebates of real taxes paid. If you are going to eliminate the amount of taxes in the FCA allowance that are rebate of paid taxes, you should do the same for the EITC and Child Care to get an apples to apples comparison on the amount of actual welfare.
My point was that the $66B and $52B figures are both worst-case figures for "welfare" -- with welfare defined as getting money back when nothing was paid in taxes.
The $66B FCA would not be entirely "welfare" just as the $52B is not entirely "welfare". Those poor families ARE going to buy milk, groceries, and other items that will collect the FairTax, so they will have paid in some FairTax and the entire FCA will not be welfare. At the same time, there are some EITC and Child Tax Credit recipients which are being refunded more tax than they ever paid.
The point is that the numbers are in the same ballpark, and the FCA does not constitute a huge growth in welfare. It is largely equivalent to the EITC and Child Tax Credits for the poor, and to Income Tax refunds and effect of the Deductions for the rest.