Your son's child and your nephew are second cousins.
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 son and your nephew, or niece, are first cousins to each other.Your son and your great nephew (the son of your nephew or niece) are first cousins, once removed, to each other.Your grandson and...
Your mother's nephew's son is your first cousin once removed.
Yes. Your nephews son will be your great nephew.