Answer:
Families are the primary sampling units and the children are the secondary sampling units.
Explanation:
Primary sampling units are described as one of the sampling units that are being selected at the beginning i.e, the first stage related to a multi-stage sample that eventually leads to select different individual participants. The primary sampling unit is also denoted as "PSUs".
Secondary sampling units are described as one of the sampling units that are being chosen in the second stage related to the selection and is also denoted as "SSUs".