"I just tried to file back taxes"
It is not clear how you tried to file back taxes. If you tried to use the online software for any year other than 2019 you were making a mistake. The online software was ONLY for 2019---no other year. 2017 and 2018 have to be prepared using desktop software and they have to be printed, signed and mailed in separate envelopes.
Further complications now are that the deadline to file a 2019 return for the first time was October 15. If you tried to e-file a 2019 return by that deadline and it was rejected, you have until October 20 to fix it and e-file it again. But you have a Social Security number problem if someone claimed your child, and the reason for that rejection cannot be fixed, The only way you can file your 2019 return claiming your children is to print, sign and mail the return. But .....that 2019 return cannot have income from the other years on it. Only your 2019 income can be on that return. If you made a mistake and included the "back taxes" on the same return you must delete the income for any other year and mail a return that has only your 2019 income on it.
To prepare and file 2017 and 2018 you need to download desktop software and prepare two other returns--one for 2017 and one for 2018, which you must mail in separate envelopes.
https://turbotax.intuit.com/personal-taxes/past-years-products/
So...again.....claim your children on your own tax returns. Mail the tax returns. Then let the IRS sort it out.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
