I believe children born in 2020 will still qualify for the first stimulus payment. This says....
"......plus $500 for each qualifying child you had in 2020. You received all your recovery rebate in 2020."
https://www.irs.gov/newsroom/recovery-rebate-credit
If your child was born in 2020 see question 9. The first stimulus check was based on 2018 or 2019 and didn't include children born in 2020 but you will get credit for them on your 2020 tax return filed in 2021.
https://www.irs.gov/newsroom/economic-impact-payment-information-center-topic-a-eip-eligibility
