(petitioner filed for Chapter 13 and listed certain tax refunds as debts owed to the debtor and claimed an exemption for such refunds; debtor subsequently filed tax return showing no tax liability and certain refundable credits comprising the federal and state refund owed debtor (which included a refundable child tax credit of I.R.C. Sec. 24); court determined that debtor's refund resulted from overpayment of tax rather than the child tax credit; trustee's objection to debtor's claim of 100 percent exemption in child tax credit, to extent not moot, is sustained because child tax credit not property of debtor's bankruptcy estate; additional child tax credit not exempt as "public assistance benefit").