Final answer:
The family structure described with a married couple, their newborn son, and the husband's daughter from a previous marriage is best classified as a married-blended family.
Step-by-step explanation:
The family described in the question consists of a married couple with their newborn son and the husband's daughter from a previous marriage. The best term to describe this family is a married-blended family. A blended family is one where there is more than one origin point for the members. This often occurs when adults with children from previous relationships remarry, bringing together children from previous unions into a new familial structure. In contrast, nuclear families are generally comprised of the parents and their immediate offspring only, while extended families include a broader range of relatives such as grandparents, aunts, uncles, and cousins living together or maintaining close relationships.