hipfake08;5087726 said:
Do they still offer the Mint tour - printing money?
Yep. Haven't been in a looong time, but remember it as one of the cooler field trips when I was a kid (although not nearly as cool as the FBI building tour, which sadly they don't do anymore). It's also something you can do in about an hour--which if you're doing things with young kids (and short attention spans) can be just about right.
Gotta do Smithsonian (Nat History and Air & Space at a minimum, but tons of cool stuff at American History too). They have a Discovery Theater for kids on weekdays that's fun. I don't know that I'd schlep out to Dulles for the other Air & Space unless you're going to be in the area for a while and have a whole day to spend on one thing.
Spy museum is awfully cool, too. They have some features there to keep kids interested throughout, but plenty for the adults to enjoy, too.
It's free to get into the National Zoo. Not the best one I've ever been to, but kids always seem to enjoy it.
I've heard lots of good things about the Newseum, but haven't made it there yet.