re: Washington DC trip with kids (10 & 12yo)

Are you renting a car?

If not check out the metro line. The Franconia-Springfield metro stop is a nice and relatively cheap area to get a hotel/motel. You can be almost anywhere in the city in a sub 30 min train ride (including Reagan Int'l.) If you stay at a hotel near one of the last metro stops you could take the metro from the airport to your hotel and around all the DC areas and never bother with renting a car.

I formerly lived in the Quantico area. DC is a great place for kids to visit