What should I call my cousin's child?

Nephew or niece. Cousins refer to the relationship between uncle's children and your own cousins, belonging to the same generation. Cousin's child is twice as young as himself and should be called cousin's nephew or niece. If my cousin's child is a girl, she should be called a niece. If my cousin's child is a boy, he should be called a nephew. Cousin's children should call themselves aunts or uncles.