My earned income tax credit and my child tax credits don’t add up to equal my total refund. My total refund is less than those two added together. How do I get the ACTC

I’m not sure what the additional child tax credit is or how to get it. And my earned income tax credit and child tax credits aren’t adding up when I add them together. And for some reason I’m only getting $700 something for all 3 of my children.