Let's see if I understand ... you filed a return with a balance due.   Did you pay it ? Do you have proof of payment ?   A cancelled check or bank/cc statement ?

And then amended the return to switch dependents which resulted in a no change 1040X? 

And then you got a bill for the unpaid balance due from the original return ?  Line 16 of the 1040X reports the amount you paid on the original return so it assumes you paid it unless you change that figure.  

Look at the form 1040X …

Column A should have the figures from the original return, Column C the corrected figures and Column B the differences between the other 2 which needs an explanation on page 2 of the form 1040X.

If you completed it correctly you will see an entry on either line 16 OR 18:

On line 16 should be the amount you paid with your original return. 

On line 18 should be the amount of your original refund you received.

Then you will see your extra refund on line 22 OR  the new balance due you need to pay on line 20.

Critter-3, thanks for the response and explanation.

- on your first question, yes I paid the amount due when I first filed my taxes on 07/13/20.  It was pulled from my bank account and I see both payments to the IRS (the 07/13/20 and then a second withdrawal / payment on 10/15/20)

- on question 2, correct the only change was which child I claimed on my taxes.  The amend return states "Your federal tax return (Form 1040-X) shows a balance due of $0.00."

- on question 3, line 16 shows the amount I paid on the original amount (amount paid on 07/13/20).  On 10/15/20 (when I electronically filed my amended taxes) the same amount was withdrawn from bank account again.

- I looked at the 1040X again, line 16 shows the amount I originally paid.  On line 20 and 22, they are blank.

I am starting to think this may have been a glitch with TurboTax as the returns look correct.

Well efiling amended returns is brand new and it is bound to have glitches ... so it sounds like you accidentally authorized the payment a second time when it was not required ... so when the IRS figures out you paid twice they will normally refund the excess.