I live in DC and the homeless thing bugs me too. The only positive thing I see on the street that helps the homeless is a newspaper called "street sense". Its a paper the covers issues of the homeless that is written by the homeless, and it includes poetry, photographs and artwork for the homeless. Its also used as a means of support, registered homeless sellers keep 75 cents of the 1 dollar cost of the paper and must check in sober and be actively involved in programs that help get them off the street.
Other than that...just tell everyone in your family DO NOT GIVE ANY MONEY to pan-handlers. They can make about $100 a day in a decent location.