‘For the 2020 tax year, there are special rules due to coronavirus: You can use either your 2019 income or your 2020 income to calculate your tax credit, and you can use whichever number gets you the bigger tax credit. (This is also the case for the Earned Income Tax Credit.) Be sure to ask your tax preparer to run the numbers both ways’. (https://www.nerdwallet.com/article/taxes/qualify-child-child-care-tax-credit).
If your earned income was higher in 2019 than in 2020, you can use the 2019 amount to figure your EITC for 2020. This temporary relief is provided through the Taxpayer Certainty and Disaster Tax Relief Act of 2020.