I think it’s a cousion but I don’t know how it works?
Answer 1
Great-niece or great-nephew. Your aunt is your baby’s great aunt.
Also, the relationship between her baby boy and his aunt is twice first cousin.
First cousins because they share great-grandparents as ancestors, but not grandparents. (First graders share grandparents and siblings share parents).
They are deleted twice because they are separated by 2 generations. (you are one generation away from your baby, your aunt is a second generation away).
There is for your baby your aunt’s niece/nephew who is a twice removed second cousin.
answer 2
Your baby would be your aunt’s great-niece or great-nephew.
Your aunt would be a great aunt to your baby.
answer 3
Great-nephew or great-niece.
answer 4
Great niece or nephew
Answer 5
Great-niece or great-nephew.
Answer 6
nephew or niece