Re: JW in DC
I've stayed there four or five times in the last few months. it's a really nice hotel, but I'm not sure it's "kid friendly". It's only a short walk to the WH, and the mall. And, since you're there, all the Smithsonian museums. The Federal Triangle Metro (Orange, Silver, Blue) is about 1 1/2 blocks away. If you get a room on the Pennsylvania Ave side, the view is fantastic, especially at night!
The lounge (as someone mentioned) may not be open on the weekend, and also, I can tell you, it is *small*, but if weekend, the point is moot.
I stay on business and use the Metro constantly, so that's a consideration for me, but maybe not you. The Rosslyn properties are indeed pretty close to the Metro, as are the Crystal City properties (one almost on top of the Metro). Also, the RI in Bethesda (low points) has no lounge, but they do have breakfast, and it's only a block away from the Metro, but it's farther from the city, but if you're Metro-ing it, it's not an issue. The Wardham Park Marriott is right next to the Metro, and only a short walk to the zoo.
it really depends on how much your kids can tolerate a walk, because, you can, and will, walk a lot.