Sarah and Luke are sister and brother. But what are their children to one another... and who is "once removed"?
The answers lie in the generations. It begins with children. The children of siblings are first cousins because they are the first generation of cousins. The children of first cousins are second cousins to one another. And so on through the generations.
"Once removed" doesn't indicate that a cousin was ever banished from the family--just that the cousins are separated by a generation. So when your first cousin has a child, you and that child are first cousins once removed.Your children and your cousin's children are second cousins. By the time people reach grandparenthood, almost everyone will probably be introducing one another as "cousin," which is both polite and correct.