A nuclear family, elementary family or conjugal family is a family group consisting of parents and their children (one or more). It is in contrast to a single-parent family, the larger extended family, or a family with more than two parents. Nuclear families typically center on a married couple which may have any number of children. There are differences in definition among observers. Some definitions allow only biological children that are full-blood siblings and consider adopted or half and step siblings a part of the immediate family, but others allow for a stepparent and any mix of dependent children including stepchildren and adopted children. Some sociologists and anthropologists consider the nuclear family as the most basic form of social organization.