How much is the child/dependent amount for what?
The maximum that can appear in box 10 of your W-2? The maximum in expenses that can be deducted on form 2441? The maximum credit for which you can take a credit on form 2441?
Please give us some details so that we can help you.
There is no fixed amount per child. Your refundable credits are calculated based on the amount of your earned income. It consists of two parts: The Earned income Credit (EIC) is looked up in this table https://apps.irs.gov/app/vita/content/globalmedia/earned_income_credit_table_1040i.pdf. The "Additional" Child Tax Credit is calculated on form 8812, but is basically 15% of your earned income over $2500, up to $1400 per child. https://www.irs.gov/pub/irs-pdf/f1040s8.pdf .
The $2000 Child tax credit, you may have heard of includes a $600 non-refundable portion. The ~$4000 figure you may have heard about was the exemption deduction, from previous years. It was not a credit, but a deduction from income before tax is calculated. Starting in 2018, that is no longer available.
For children over 16 and other non-child dependents, there is a $500 (non refundable) other dependent credit, rather than the Child Tax Credit. Your children 17-18, and full time students 19-23 still qualify you for child based EIC.