The letter from IRS regarding form 8812

I received a notification from IRS that mentions I owe money (it is a whole amount of my received advance child credit payments plus interest). 

Here are those possible reasons listed in the letter:

1. The computation of the credit on Schedule 8812 was incorrect.

2. The amount on Schedule 8812 was not transferred correctly to the tax return.

3. The reconciliation of advance child credit payments was incorrect.

 

I did transfer received advance child credit payments to my tax return.

However, I noticed that number on Line 30 (the number of qualifying children taken into account in determining the annual advance amount you received for 2021) is incorrect.  It is a number 2 on line 30. While I have 3 kids (two of them are under 6 years old) and they are all listed as Dependents (I checked).

The number of qualifying children in box 2 of my Letter 6419 from IRS is 3.

 

I'm confused as to how TurboTax calculated the number of children on line 30. Is it possible that it could be a bug in TurboTax? I entered 3 children everywhere but TurboTax put 2 on line 30. Could it be the reason why I received this letter?