You can use the phrase next of kin to describe your family members, especially those who are closely related to you, like your children, spouse, siblings, or parents. It's most common to talk about someone's next of kin when the person has been injured, is terribly sick, or has died. For example, a nurse in a hospital might say, "I'll call his sister to let her know how he's doing — she's listed as his next of kin."