The Arlington Cemetery is one of the places I would recommend that you see at least once in your life. I have been to D.C. about three times previous to the visit in February 2006, but had never been. It's a huge, huge area, didn't realize until I saw it, how big it actually was. It really gives you a funny feeling that I can't explain, because I'm sure it's different for everyone, while you're walking down the path. We were able to see the changing of the guard at the Tomb of the Unknown Soldier, which was an experience in itself.
I wouldn't necessarily recommend this for children, unless they're older, because I don't think they'd appreciate it. I also recommend that you take the tour, because it's hard to walk. We walked and I promise you there's a lot we were unable to see.