They can receive emergency help at these places I know of, there are probably quite a few others, many at churches.
Western Fairfax Christian Ministries
http://wfcmva.org/ in Chantilly near PO, one time emergency depending on food and other resources available, otherwise have to be qualified by Fairfax County Department of Social Services to get food and other services.
Food for Others
https://www.foodforothers.org/neighborhood-sites/ - just bring grocery bags at sites and times listed, mostly in central Fairfax County, no FCDOSS qualification needed.
Sites are accessible by Fairfax Connector buses
http://www.fairfaxcounty.gov/connector/routes/ Fare $1.75