Turbotax 2018 review of numbers does not add up in the presence of child tax credit

Hello,  

I understand more details maybe required but let's start with following numbers.

In Turbotax 2018, toward the end, where it shows "Let's Review Your Numbers", shows "How We Calculate Your Federal Refund".

And lists following,

Your taxable income $161,179

Federal Credits We Found For you $5,000

Federal Taxes You Owe $19,358

Federal Taxes You've Paid, Plus Certain Credits $18,664 <<----- this number is also in Box 2 in my W2 (Federal income tax withheld with married, federal exemptions of 4)

And the math is,

And $18,664 - $19,358 = -$694 as federal tax due.

Turbotax 2018 shows i have $5,000 child tax credit.

So, why isn't $5,000 applied to -$694 to reduce my federal tax due to $0 ?

What am i overlooking about how the child tax credit works?

Is the federal tax i've paid (withheld) somehow includes (portion) of child tax credit?

Thanks much.