The point of citizenship is a good one, but illegal children with ITIN get $1000 as child tax credit or additional tax credit.
Last time, I prepared a 1040 for a married couple and a child, all of them had ITINs, the IRS sent a letter because I didn't claim the child tax credit and additional child tax credit. I called the IRS and they asked me to amend the return and the parents got the $1,000 credit.
For clarification, the father is not involved at all either because he does not file US taxes, he is not in the US or both. Support is not an issue.
I am also assuming the uncle qualifies for HH and the child tax credit.
We also need to post more questions to this board since we should clarify a lot of issues before next tax season.