Before visiting the Capitol, have a discussion with your kids about Congress's role in the government and the Capitol's place in history. Then during the tour, encourage them to move up front to see and hear better.
Kids can email the president at firstname.lastname@example.org or send a letter to the White House. The president and first lady even have their own zip code: 20500.
Kids get a kick out of seeing currency printed at the Bureau of Engraving and Printing. At the gift shop they can buy bags of shredded bills and get a postcard-size rendering of a dollar with their face in the place of George Washington's.