Frequent DC traveler, so I've done the summer crowd thing from time to time - I carry an umbrella everyday, regardless of forecast, having been caught in a downpour one day when I trusted Ms Weatherperson it would be a sunny day. When it rains in DC, its serious rain. If I had kids with me who can't hold their own umbrellas, I would pack some cheap 99 cent ponchos for the same contingency.

A good DC map is the laminated one that covers central DC, that folds out to an 8x10 and folds down to a third of that. Available at most tourist stops, and pretty good versions in any city before you arrive. If you are driving it can pay to have a map with the direction of traffic on the major roads, there are some one ways.

Also second the visit to Arlington, particularly if you know someone buried or remembered there. I was able to find my brother's friend who died in Nam and an uncle who died in the Pacific in the last days of WWII. Both were very sobering experiences for me, totally unexpected.

EDC for sun burn (lotion), heat (water/food), rain (umbrella etc) and blisters (bandaids etc), not for urban survival in the event of a full scale attack. Accept that you are toast if DC gets hit while your there, your rucksack will be lighter and you should be happier. If the kids get tired or lines too long, take them back to the hotel and take a nap. DC will be there tomorrow, and probably the next time to come too.