I will recommend one of the parades described here:
http://www.mbw.usmc.mil/

Visit Arlington Cemetery, with the eternal flame, changing of the guard at the tombe of the unknowns.

The Spy Museum is a great idea.

I think that a tour of the KC would be boring.

Not too far from DC is Great Falls of the Potomac. It is a National park service facility with hiking trails along the C&O canal. Some locks etc., a place where the kids could get some energy run off and if it has been wet, the falls are fantastic.

There are buses to Annapolis. I know people who commute to the District from there. Naval Academy and nice waterfront.

CGS said above -----'There's also a great little quirky art museum across from the White House - unfortunately the name escapes me but it's a craft museum and the name starts with an "R".'


That would be the Smithsonian's Renwick, a branch of the American Art Musuem and one of the city's lesser-known gems.
http://americanart.si.edu/renwick/
It has a beautiful collection of crafts (glass, basketry, textile, wood) in a fabulous late-19th century mansion.

Get them high!

Go to the top of the Washington Monument

OR

the bell tower of the Old Post Office Building

for some fantastic views of the city.

FYI, if you are going up the Washington Monuments, tickets are almost sold out for the month (based on my try yesterday, 1 out of the 6 days we are going to be there had availability)so get your tickets ahead of time.

Meant to add that I agree with the suggestion of a trip to the Inner Harbor in Baltimore. The Aquarium is great, Camden Yards is a great park. These would balance out the trip between history and just plain fun. The Maritime Museum (while another museum) has a submarine, Coast Guard Cutter and an old sailship that you could tour.

Take the metro (subway) - you can even pop across the river to Arlington Cemetary - and easily spend half a day there. The metro has many stops in DC proper, and heads out to the suburbs too. It is quite an interesting adventure and the transportation is fast, and inexpensive.

Another thought is that the national park service runs a tourbus on the mall which you can hop on and off of as much as you like during that day. The bus does a giant loop around the mall, pointing out interesting and lesser known things that you might miss on your own. They also run a bus to Arlington Cemetary, where you transfer to another bus within the cemetary that points out landmarks and points of interest.

I agree with those who wrote visit the Old Post Office tower - great views of DC, and there is a food court at the lower floor for quick refreshments.

Do the holicost museum - it is a sobering reminder of man's inhumanity to man - but we need to see history in this tangible way. The kids perspective is very interesting. You may have to buy advanced tickets.

ESPNZone restaurant. Took my son last summer when he was 14, and he absolutely loved it. Three floors with the bottom floor being all gaming. The food was quite good, not outrageously priced, and there is a coupon in one of the tourist booklets that gives you a $5 game card for free with the purchase of the hamburger platter.

Lots of good information is available on the web, google kids and Washington DC for tons of sites. This one looked good:
http://www.thedistrict.com/takethekids.html

My 12 year old loved the Spy Museum and going to the top of the Washington Monument.

I did take her to the holocaust museum and while she did not appreciate it as much as I did - I am glad I took her. The more brutal video footage and photos are done in a way that you have to lean over the watch them - so if you did not feel it appropriate for your children you could move forward and not have them see it. I feel like PamSF does though - it is important.

The double decker buses are great. The last time i was there they offered a 2 day pass for around $30.00. The bus had stops in Georgetown, adjacent to the Zoo, Union station, the Smithsonian, Arlington. and all of the mall monuments. We rode on the upper deck in Janurary and had a blast.

How about showing them the world second longest (deepest) subway escalator--I think Russia has a longer one (I can't think of the name of the station but it is in all the travel books), the Adams-Morgan section of town with all the ethnic restaurants--go to a different one each night, food court in Union station--although kids are used to food courts in this day and age, ahh- I am still thinking-