It depends on if you share a common ancestor. If not, there is no relationship.
Your cousin's baby would be your second cousin
Your cousin's children are your second cousins
Your cousin's daughter is your first cousin once removed. Your daughter and your cousin's daughter would be second cousins.
Your cousins child is your first cousin once removed.
If you are first cousins, they would be a first cousin once removed.
Your children and your first cousin's children are second cousins.
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.
They are also your 1st cousin.
Your children and your first cousin's children are second cousins.
second cousins to his cousin's children, you'd be third cousins
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 daughter is first cousin once removed to your cousin. Your daughter is second cousin to your cousin's children. Your cousin's children are first cousins once removed to you