a) A couple, alone, or with their never-married child(ren), or
b)A lone parent with their never-married child(ren), or
c) One or more grandparent(s) with their grandchild(ren), where the middle generation is absent.
The definition of a "couple" depends on the census year. In 1971 and 1981, a couple had to be married. In 1991, unmarried, opposite-sex cohabiting couples were added, and in 2001, same-sex couples were added.