second cousins to his cousin's children, you'd be third cousins
They would be second cousins.
They would be cousins to some degree. They are 2nd cousins.
He would be your first cousin once removed; also, he would be the second cousin of your son.
They would be first cousins once removed. Your great aunt's children are the first cousins of your parent.
Your cousin's daughter is your first cousin once removed. Your daughter and your cousin's daughter would be second cousins.
Your niece and your child are first cousins. There is a difference on one generation between the two. That would make them first cousins once removed.
First cousins once removed. Your child and your nephew are first cousins and there is one generation difference.
If you are first cousins, they would be a first cousin once removed.
Second cousins
Your 1st cousin's granddaughter would be your daughter's niece.
They would be first cousins.
Your son and your nephew are first cousins to each other. Their daughters are second cousins to each other.