You are the grand uncle to any children your nephew or niece have.
They would be your grand nephew or grand niece.
If the children of your nephew/niece have children of their own, you'd be a great uncle too.
Your son and your nephew are first cousins. Your son and your nephew's son are first cousins, once removed.
Your son and your nephew are first cousins to each other.
Your son and your nephew's son are first cousins, once removed, to each other.
Your nephew is your son's first cousin. Your nephew's son is your son's first cousin, once removed.
You are aunt or uncle to your nephew, great aunt or great uncle to your nephew's son, and great great aunt or great great uncle to your nephew's grandchild.
You are a great aunt or great uncle to you nephew's son
First cousins
Great Uncle.
A niece's son calls his uncle his uncle, just like everyone else.The niece's son calls her uncle his great uncle. He is the great uncle's great nephew.
Your niece's son is your great nephew. You are his great aunt or great uncle.
Your niece's son is your great nephew. You are his great aunt or great uncle.
Your husband is great uncle to your niece's son (your great nephew).
The son of your great niece is your great great nephew. You are his great great uncle.
You son and your niece are first cousins. Your son and your niece's son are first cousins, once removed.
uncle and nephew
You are their great-uncle/aunt.
Your son and your niece are first cousins to each other. Your son and your niece's son are first cousins, once removed.
Your niece's son is your great nephew. You are his great aunt (if you are a woman) or his great uncle (if you are a man).
The son of your great niece is your great great nephew. You are his great great uncle.
Your sister's daughter is your niece. If you are a woman, you are your niece's aunt; if you are a man, you are your niece's uncle. Your sister's son is your nephew.