I had this problem and finally solved it. TurboTax automatically claimed the Family Tax Cut as soon as I had told them I had kids and was filing with my wife. Later when I got to the screen to "claim it" and did, I saw no impact on my amount owing/refund amount and thought it was not calculating. But then, if I went back and did not claim it, my takes owing shot up. Then I claimed it again and saw it go back down to the initial number.
