I am not sure what your question is but if you received Letter 6419 enter the information as it is stated in Letter 6419. As long as all your children are listed on your return you will receive the full Child Tax Credit you are entitled to. That is most likely why your return says you have $7,500 of Refundable Child Tax Credit on Line 28. As long as this number is equal to your total Child Tax Credit less what you were paid, then you are getting what you are entitled to.
As for Letter 6475, as long as you report the amount you received, you should be fine.
I have no idea why I do not understand why it is still saying I only have 2 when I have had three since these economic relief payments started in 2020. I would not be concerned with this at this time as long as you are receiving all that you are entitled to through your 2021 return. Sometimes we cannot explain or understand why the IRS records show what they show.
