The IRS has posted that if you did not get the full stimulus you are entitled to then your ONLY option is to wait for the 2020 filing next year.
Go to this IRS website for information (Question 29) - https://www.irs.gov/coronavirus/economic-impact-payment-information-center
A29. Payment amounts vary based on income, filing status and family size. If you filed a 2019 tax return, the IRS used information from it about you, your spouse, your income, filing status and qualifying children to calculate the amount and issue your Payment. If you haven’t filed your 2019 return or it has not been processed yet, the IRS used the information from your 2018 return to calculate the amount and issue your Payment. The IRS is not able to correct or issue additional payments at this time and will provide further details on IRS.gov on the action people may need to take in the future.
If you did not receive the full amount to which you believe you are entitled, you will be able to claim the additional amount when you file your 2020 tax return. This is particularly important for individuals who may be entitled to the additional $500 per qualifying child payments. We encourage everyone to review our “How do I calculate my EIP Payment” question and answer (See question 21).
Keep the Notice 1444, Your Economic Impact Payment, you will receive regarding your Economic Stimulus Payment with your records. This notice will be mailed to each recipient’s last known address within a few weeks after the Payment is made. When you file your 2020 tax return next year, you can refer to Notice 1444 and claim additional credits on your 2020 tax return if you are eligible for them. The IRS will provide further details on IRS.gov on the action they may need to take.
If you used the non-filer site and did not get the stimulus money for your children, you have another chance if you go back to the non-filer site by September 30.
Use the Non-Filers tool by September 30 if you have not already given us your qualifying child’s information to get a $500 catch-up payment. For information about qualifying children, see our Economic Impact Payment Information Center.
I tried the non-filer tool today 9/19/2020 and it was not accepted because I have already received my 2020 tax refund. I also received the @$2400 for my husband and myself but not the $500 for our kids (2). Not sure what else I can do.
@lock041614 If you actually filed a tax return and received an income tax refund, you cannot use the "non-filer" site. You are not a "non-filer". Sorry--you are among the people who simply will have to wait until you prepare and file your 2020 return in 2021 to get stimulus money for your children unless the IRS comes up with a way to fix it sooner.
If you already filed a return and/or filed a non filer return then the "last chance" non filer option on the IRS site is not going to work for you ... this is ONLY for those who will not file and have not yet filed a 2019 return.