If my child turned 17 on December 27th, 2020 then why do i not get the child tax credit for her? Instead it put her in as just a dependent. Is this correct?

[DoninGA]

If the child was 17 or older at any time in 2020, including 12/31/2020, they are no longer eligible for the Child Tax Credit.  They are only eligible for the Other Dependent tax credit of $500.

[Opus 17]

Remember, you got the full tax benefit for the child in the year they were born, even though they were only alive for four days.