You find this credit on Form 1040, line 18b, and will see it on supporting schedules and forms, as well.
The additional child tax credit is reported on line 18b of Form 1040 and would also be found on Form 8812 and Schedule 3. It is up to $1,400 per child and is the portion of the child tax credit that you can receive even if you do not have any tax charged.
The non refundable portion is up to $600 per child and is reported on line 13a of Form 1040. If you do not have taxes charged, then this portion of the credit would be reduced to -0-.
Click this article to learn more: What is the Additional Child Tax Credit?