Final answer:
The national program aimed at preparing young children for school by providing various foundational services to disadvantaged families is known as Head Start.
Step-by-step explanation:
The federally funded, national program designed to promote school readiness by providing educational, health, nutritional, and social services to children aged 3, 4, and 5, particularly to those from the nation's poorest families is B) Head Start.
Head Start is a program aimed at early childhood education for families with limited educational and financial resources. This crucial program forms part of the United States government's safety net programs, alongside other assistance initiatives such as WIC, which provides food aid to pregnant women and newborns, SNAP, commonly known for providing nutritional support through what was formerly known as the food stamp program, and Medicaid, which offers healthcare coverage to low-income individuals.