Special Olympics is often looking for people to volunteer to cheer at their events. Could be a fun whole-family activity:
http://specialolympicsva.org/volunteer/volunteer-to-cheer
In Arlington, Mount Olivet United Methodist Church has a monthly community assistance program that my kids and I regularly help with. Teens can help with bagging groceries, serving the dinner, etc. Many of those being served speak Spanish so Spanish-speaking volunteers are especially needed.