Your aunt's child, son or daughter, is your First Cousin.
The same is true for your uncle's children.
a nephew's kid to his aunt's kids would be their cousin.
Presuming your son is also your wife's son, the your wife's aunt is your son's great aunt and he is is her great nephew.
Your aunt's son and her niece are first cousins to each other.
You're a Great Aunt to your nephew's son, who is your great nephew.
He is her nephew, and she is his aunt.
You will be his aunt.
He would be your son's third cousin.
You are your nephew's uncle, or aunt, and his son's great uncle, or great aunt. Your nephew's son is your great nephew.
Your aunt is great great aunt to your son's daughter (your granddaughter). Your granddaughter is your aunt's great great niece.
Your aunt's child, son or daughter, is your First Cousin. The same is true for your uncle's children.
Your son is a second cousin to your aunt's grandchildren. Your aunt's grandchildren are the children of your parent's cousins, making them second cousins to your son.
Your aunt's daughter is your first cousin, and her son is your first cousin, once removed.