There are limits to the amount of Child Tax Credit that you can receive. While the full credit is $2,000 per child, the credit itself is limited to tax liability. So, you have likely reached the limit where you have no tax liability left to reduce. Once you have reached the limit of tax liability, the refundable portion of the credit is also capped at only $1,400 (or 15% of the earned income over $2,500) per child. So, it's quite possible to not receive the full credit.
There are limits to the amount of Child Tax Credit that you can receive. While the full credit is $2,000 per child, the credit itself is limited to tax liability. So, you have likely reached the limit where you have no tax liability left to reduce. Once you have reached the limit of tax liability, the refundable portion of the credit is also capped at only $1,400 (or 15% of the earned income over $2,500) per child. So, it's quite possible to not receive the full credit.