My wife Kimberley and I enjoy the American History Museum. It has everything from old campaign buttons to the dresses of America's first ladies. Any history buff can get lost in there for hours. D.C. Parts of the city have the same crime and drug problems you would find in most metropolitan areas. Most of the people you'll run into are vacationing families from all over the nation, just like yourselves.
Parking can be a real problem.
There are few spaces available and parking tickets can be very expensive out here. I'd recommend taking the subway system called the Metro. It's clean and affordable. The Capitol South Metro stop will take you to the museums and many of the monuments. But you can still expect to do a lot of walking.