This is the last day to use the IRS Free File site to prepare and e-file a 2021 tax return. The filing deadline for a 2021 tax return was April 17, 2022. You have three years from that deadline to file a 2021 tax return and get a tax refund, but the tax return can only be prepared on paper and must be sent in my mail after November 17.
You are confusing two things. The "stimulus" or EIP payment is also know as the "recovery rebate credit." The child tax credit is an amount you can get if you have a qualified child dependent under the age of 18 who has a Social Security number and who lived in the U.S. for at least half the year in 2021.
The child tax credit shows up on line 28 of a Form 1040. The recovery rebate credit shows up on line 30.
Use this IRS site for other ways to file for free. There are 8 free software versions available from the IRS Free File site
https://apps.irs.gov/app/freeFile/