You and your first cousin's children are first cousins once removed. Your children are their second cousins.
Your children are the first cousins of your brother's children, and the first cousins once removed of your brother's grandchildren.
Your child and your sister's children are first cousins. Your grandchild and your sister's children are first cousins once removed.
Anyone descended from a brother or sister of one of your direct ancestors is your cousin. There are different names for different kinds of cousins. For example, your first cousins are the children of your aunts and uncles. Your second cousins are the grandchildren of your great aunts and great uncles. Your parents'first cousins are your first cousins, once removed. And the children of your first cousins are also your first cousins, once removed.
The first cousin of your dad's first cousin is also your your dad's first cousin or is not related to him or to you. The children of two first cousins are second cousins to each other. So the son of the first cousin of your dad's first cousin is either your second cousin, or is not related to you at all.
Your granddaughter and your first cousin's grandson are third cousins to each other. You find their common ancestor that is, your grand parents, and count the number of generations separating them, there are Brother and Sister then cousins, you and your cousin would be one (first cousins), your children and your cousins children are second cousins and their children are third cousins and so on.
Your first cousin and your grandchildren (your child's children) are first cousins once removed.
The children of your great grandfather's brother are your grandparent's first cousins, and your first cousins twice removed.
The children of siblings are first cousins, so your daughter and your brother's daughter are first cousins to each other.
The children of your wife's first cousin are her first cousins, once removed. They are not related to you.
Your sister's children's children are her grandchildren.Your children and your sister's grand children are first cousins, once removed.Your grandchildren and your sister's grandchildren are second cousins.
All the children of your aunt and uncle are your first cousins. You and your siblings are their first cousins, because you are the children of their aunt or uncle.Your first cousins children are your first cousins, once removed. Your children are first cousins, once removed, to your first cousins.Your children and your first cousin's children are second cousins to each other.
Your first cousins childrens are your second cousins.