Great Falls is a good place for a picnic. The Mall is lousy in the summer, to crowded, dirty, etc. I do suggest that you guys do the monuments by night, esp. the Thomas Jefferson Memorial & the FDR Memorial. Was there last night showing my sis from RI around, & they look great. Also an option, renting a boat on the Potomac waterfront. Right under the Key Bridge is a place you can rent conoes, moterboats, etc. Word of warning, make SURE you park somewhere where you won't be towed. Last night driving through Georgetown, we watched tow-trucks have a jolly time making sure some people's evennings were going to take a turn for the worse, and they have nightwork, but that's only during the weekdays. Well, that's about all the advise I can think of... Oh, wait, also it gets REALLY humid & hot down here, so bring light loose clothing (sorry guys, I know ya'll wanted to show off in a'la Ricky Martin type shirt & pants, but you'll be miserable).
Anyway, back to my Harry Potter (almost done :-) )