Children of your cousin are actually called your “first cousins once removed.”
Your cousin’s child is NOT your second cousin as is commonly believed. The appropriate name for addressing your cousin’s child is niece or nephew, even though they are actually first cousins once removed.
What does “Once Removed” Mean?
The term “once removed” indicates the number of generations away from you. For example, your cousin’s children are one generation distant from yourself; hence, first cousins “once removed.”
What are “Second Cousins” then?
Children of your cousin are second cousins to your own children. First, second, and third cousins each represent a different generational level. First cousins share the same grandparents. Second cousins share the same set of great grandparents.
Using Generations to Define Family Relations
Think about family relations like a layer cake: Each layer is a generation. The first layer of kids are all siblings, and the next layer of kids are all first cousins. Within the next generation (or layer), they are all second cousins.
If you move BETWEEN layers on the cake, use the term “removed.” Once removed is one layer away, twice removed would be two layers, or generations away. Since your cousin’s child is a different generation, hence the term “once removed.”
TEST: What relation is your first cousin’s once removed child to you? Move two layers on the cake….your first cousin twice removed!