If you have to choose, the Capitol Building is a better tour than the White House, less waiting & more open to the public, although I haven't been through the process since they put in the underground Visitor's Center. The Air & Space Museum is kid-friendly. See the IMAX movies there, gives everyone a chance to rest out of the heat, which might be oppressive in August, or maybe you'll be lucky. Some of those days seem a little ambitious - lots of travel while touring on the way, but maybe you're from hardier stock. Good luck, I've enjoyed all the places you mentioned, although never on a single trip.
