You say your children turned 18 in 2021? You can still claim a child of age 18 as a qualified child dependent. Did you enter them as dependents? Did they file tax returns already and say they cannot be claimed? That is common mistake made by kids who do not know they will mess up their parents' tax returns by saying that. If one or any of them made that mistake---they have to amend their tax return and change the way they answered the question in My Info about being claimed. But you do not have to wait for them to do that. Your own return that claims them has to be printed, signed and mailed. The kid's SSN will remain in the system as having been used so you will never be able to e-file this year.
When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.
Federal and state returns must be in separate envelopes and they are mailed to different addresses. Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.
WHO CAN I CLAIM AS A DEPENDENT?
You can claim a child, relative, friend, or fiancé (etc.) as a dependent on your 2021 taxes as long as they meet the following requirements:
Qualifying child
Qualifying relative
When you add someone as a dependent, we'll ask a series of questions to make sure you can claim them. There may be other tax benefits you can get when you claim a dependent.
For the kids