Cousin once removed.
The children of your mother's first cousins are your second cousins. The children of your mother's second cousins are your third cousins. And so forth.
Your mother's sister's children are your 1st cousins.
Your uncle's grandchildren are your first cousins, once removed. They and your grand children are your second cousins, once removed
Your children and your first cousin's children are second cousins. Your children and your second cousin's children are third cousins. And so forth.
Your son and your nephew are First Cousins. The children of your nephew and the children of your son are Second Cousins to each other.
Your first cousin's children are your first cousins, once removed. They are your children's second cousins. Your second cousin's children are your second cousins, once removed. They are your children's third cousins. And so forth.
Your children and your first cousin are first cousins, once removed, to each other.
Your first cousin's daughter and you are first cousins, once removed. Your first cousin's children and your children will be second cousins to each other.
Your children and the children of your first cousin are second cousins to each other.
Your daughter and your first cousin's children are second cousins to each others.
Your mother's sister's children, sons or daughters, are your first cousins. The children of first cousins are second cousins to each other. That is the relationship between your children, or either sex, and your first cousin's children, of either sex..
Your child and your great nephew's parents would be first cousins. Their children would then be second cousins. And if they have children, they will be third cousins.