Your first cousin and your grandchildren (your child's children) are first cousins once removed.
You and your first cousin's children are first cousins once removed. Your children are their second cousins.
The children of your wife's first cousin are her first cousins, once removed. They are not related to you.
Assuming both children are on the same side of the family, your child's first cousin is a second cousin to your first cousin's child. Your child is also a second cousin to your first cousin's child. Your child can have first cousins who are not related to your first cousin and thus not related to your first cousin's child.
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 First Cousin and your children are related as First Cousins once removed.
Your niece is the first cousin of your children and the first cousin, once removed, of your grandchildren.
The nephews of your first cousin once removed, like the children of your first cousin once removed, are your first cousins twice removed.
Your father's brother is your uncle. Your uncle's son is your first cousin and your children's first cousin once removed.If your first cousin has a child, that child and your children are second cousins.
The children of your father and the children of your father's first cousin are second cousins to each other. The children of your father and the children of your father's second cousin are third cousins to each other.
Your first cousin once removed is the child of your first cousin. Let's call her Jane.Jane's first cousin may be the child of your first cousin's sibling. If so, that would also be your first cousin once removed.However, in order to produce Jane, your first cousin married someone. That person will have siblings whose children are also Jane's first cousins, but who are not related to you at all.So, the first cousin of your first cousin once removed is also your first cousin once removed, or is not related to you at all.
You would usually call the children of your husband's first cous by their name. They are not related to you. If you need to refer to them in a general sense, you might call them your husband's first cousins once removed.Yuor husband's first cousin's child is related to you children as a second cousin.
Your first cousin's child would be your second cousin