A household can contain one or more families. In a multiple family household, one family is called the primary family.
Where there was more than one family in a household on Census Night, the family with dependent children is designated as the primary family. If there was more than one family, and no children were present in the household, then the first family identified on the Census form becomes the primary family.
See also Child, Family, Household, Relationship in Household (RLHP).