Hi - Thank you for the tips.
I always e-File. Looking back at my saved TurboTax files, my 2 youngest have X marks on "Qualifying Child for Child Tax Credit" for last two years. Going back another year, my 3rd child has the X mark. I'll have to grab my 2017 PDF\backup and look through it. However, considering that I import the prior year's info, it's very likely this issue has been going on for awhile.
Looking through my records, I don't appear to have form 8812. Weird.
I read about the requirements at https://turbotax.intuit.com/tax-tips/family/what-is-the-irs-form-8812/L1HbgYQqE and nothing stood out as to why I wouldn't have a form 8812.
I've got more investigation to do once I get to my system with TurboTax loaded on it.
