Typically, the child tax credit box is not checked if the children are too old for the credit (over the age of 16) or if they do not qualify for some other reason, such as they are being claimed by another person.
If your children are 16 years old or over, they do not qualify for the additional payment under the Economic Impact Payment.
If they are under 16, you may wish to amend your tax return - because you want to be sure you get the proper credit on the tax return itself - by filing Form 1040X.
Amended returns are filed by mail and typically take up to 16 weeks to process. Processing times right now are significantly delayed due to reductions in staff.
It is not known if, upon processing, an advance payment will be sent.
Any taxpayer whose advance payment received is less than the full payment for which he or she is entitled, will be eligible to claim the difference as a credit on the 2020 tax return filed in 2021.
Please check these links frequently for updates: