All first and second Economic Impact Payments have been sent out by the IRS. If you didn't get a first and second Economic Impact Payment or got less than the full amounts, you may be eligible to claim the 2020 Recovery Rebate Credit by filing a 2020 tax return if you have not filed yet or by amending your 2020 tax return if it's already been processed. Your Recovery Rebate Credit on your 2020 tax return will reduce the amount of tax you owe for 2020 or be included in your tax refund. Here's how eligible individuals claim the credit:
in other words, file a 2020 return even if you are not required to. You may also want to include an identity theft affidavit form 14039 for each of your kids that was claimed by somebody else.
https://www.irs.gov/pub/irs-pdf/f14039.pdf