As xmasbaby pointed out, you are using TurboTax to prepare the 1040, as that is the tax return itself and what is sent to the IRS to get your refund.
You should be able to "preview" your 1040. If you do that, you can see your total income tax on Line 11. The credit for Grandma and the Credit for daycare can ONLY offset that amount. Also, $1200 of the credit for the other two children can ONLY be used against that amount. So most likely, that is what is limiting things.
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Yes, TaxCaster is only an estimate, and lately has given some rather inaccurate estimates.
