Don't waste time on the museums.
I'm going to have to strongly disagree on this one. To begin with, all the Smithsonian Museums & National Gallery of Art are FREE, quite different from the private museums elsewhere. Most of these museums are along the Mall and can be mixed in with visiting the monuments there. Depending on the weather, the air-conditioned comfort of a museum can be a welcome alternative to a hot hike to the next monument. They also have far superior dining & restroom options than the monuments.The Air & Space Museum is usually a hit with all ages - see the movies there, too. The Museum of American History is also a favorite, but there are a lot of options, YMMV.
The National Zoo - not on the Mall, but accessible via METRO - is also worth a trip if weather cooperates. Pro Tip: Get off METRO at the Cleveland Park Station, but return via the Woodley Park/National Zoo Station. The Zoo is is just about equidistant from these two stations, but this way your walk is downhill both ways.
By all means go the orientation meeting about touring DC. It may seem tricky, but with a little planning you'll maximize your fun.