It depends...they may be no relation at all, or your cousin, or even your brother or sister.
For instance: your cousin's cousin may be your father's brother's son's mother's sister's daughter! In that case you are not related at all.
However, your cousin's cousin may be a mutual cousin to both you and your cousin.
Or your cousin's cousin may refer back to either yourself or a sibling.
Your cousin's sister is also your cousin. If she is your first cousin, second cousin, etc., then her daughter is your first cousin, or second cousin, etc., once removed.
If your cousin is your first cousin once removed, or third cousin twice removed, or some other type of cousin with a removed relationship, determining your relationship to the daughter is a more complex problem and there will be two very different possibilities. For example, the daughter of your second cousin once removed could be either your second cousins twice removed or your third cousin, depending on whether you are in a younger or older generation than your second cousin once removed.
Your grandchildren and the children of your first cousin are second cousins, once removed, to each other.
Your children and the children of your first cousin are second cousins to each other.
Your grandchildren and the grandchildren of your first cousin are third cousins to each other
You and your father's first cousin are first cousins once removed.
You and your father's second cousin are second cousins, once removed.
Your and your fathers first cousin, once removed are either second cousins or first cousins twice removed.
Could be anything from sisters to first or second cousins to no relationship at all if they do not share a common ancestor.
If you mean between you and your cousin's children, you are first cousins once removed.
Your first cousin's child is your first cousin once removed.
You and your first cousin's child are first cousins, once removed.
You and the son of your second cousin are second cousins, once removed.
Your children and your niece are first cousins to each other.
The children of first cousins are second cousins to each other. Where two people are first cousins to each other (call them Joe and Ed) Joe's children and Ed are first cousins, once removed, and Ed's children and Joe are first cousins, once removed. Joe and Ed are in the same generation. Their children are in the next generation. "Once removed" refers to people who are in different generations and there is only one generation difference between them, as is the case with parent and child. Grand parent and grandchild, for example are two generations removed from each other.
The offspring of your first cousin is your first cousin once removed.
Nephews are the sons of your brother or sister. Therefore nephews who are not brothers to each other are first cousins to each other.
Your grandson and your sister's grandson are second cousins to each other.
The relationship between your sister's (or brother's) child and your cousin is the same as the relationship between your child and your cousin. Your child and your first cousin are first cousins, once removed. Your child and your second cousin are second cousins, once removed, and so forth.
Your cousins child is your first cousin once removed.
Your child and your first cousin's child are second cousins. Your child and your second cousin's child are third cousins to each other.
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.
Your first-cousin and your child are first cousins, once removed.
Your son and your brother's grandchild are first cousins once removed.
Your child and your sister's daughter are first cousins. Your grand child and your sister's daughter are first cousins, once removed.
Your niece and your child are first cousins. Your niece's child and your child are first cousins, once removed. The children of your niece's child and of your child are second cousins to each other.
If it is not your common grandparent, there is no relationship.
Your child and your niece are first cousins to each other. Your child and your niece's child are first cousins, once removed.
They would be second cousins. Your child and your grandniece's parent are first cousins. There are no 'removed' involved because the generation difference between the common ancestors (your parents) is the same.
You are First Cousins