What Do I Call My Niece's Daughter?
The daughter of your niece is also your niece, but in a second degree. If you have any children, then your niece is their cousin in the first degree, or sister cousin. The daughter of your niece is to your children a second cousin, according to a regular consanguinity chart.
After the first degree of consanguinity, most family relations repeat themselves in different degrees: first cousins, second cousins and third cousins.This is also very common when it comes to parenting, where you can find sons and daughters, grandsons and grand daughters and great-grand sons and great-grand daughters and so on.