Can you clarify your situation? Why are you wanting to enter $500 and $600?
You said your child turned age 17, so the final credit calculated on your return would NOT include that child.
You also said you received less than the 'maximum', and DID receive a credit for the child (who turned age 17 in 2020). Although you won't need to 'pay back' the credit that you received for the child, that amount that you received would still be used for determining your final credit (which does not include a credit for that child).
