You should arrive early to avoid lines at the National Air and Space Museum, as this is the second-most visited museum in America. Covering the history of flight from the 18C to the Apollo space missions there are a variety of kid-friendly activities to explore including the How Things Fly exhibit, which is a hands-on educational display with a fighter plane flight simulator. Free ninety minute docent-led tours leave daily at 10:30 am and 1 pm. Closed for holidays.