What is a nuclear family

A nuclear family -  family group consisting of two parents and their children (one or more). It is in contrast to a single-parent family, to the larger extended family, and to a family with more than two parents.

Nuclear families typically center on a married couple; the nuclear family may have any number of children. There are differences in definition among observers; some definitions allow only biological children that are full-blood siblings,but others allow for a stepparent and any mix of dependent children including stepchildren and adopted children.