A child 21 years of age and under must be included in the same Food and Nutrition Services unit when living with which of the following?

The correct answer is that a child 21 years of age and under must be included in the same Food and Nutrition Services unit when living with parents living together. This reflects the guidelines set forth in food assistance programs, which are designed to assess household income and resources for eligibility. When parents live together, they are typically considered the primary caregivers for their children, and including the child in the same unit ensures that the family can fully access benefits that support their nutritional needs.

Specifically, living together implies a shared responsibility for the child's welfare, which is fundamental in determining eligibility for food assistance. This approach encourages the notion of a family unit, where resources can be pooled together, thereby resulting in a more accurate assessment of the family's nutritional needs and financial means.

Other choices do not accurately reflect the requirements for including a child in the same food assistance unit. For instance, only including natural or adoptive parents, or just stepparents, fails to acknowledge situations where parents may be non-traditional or have varying custodial arrangements. Therefore, the broader inclusion of parents living together encompasses a more comprehensive framework for determining household eligibility in food assistance programs.