Thinking of taking the Kids to Wash. DC any suggestions?

Cherry hill worked for us... close proximity to the Metro to get into DC to see all the museums and sites.

While you're close, and depending on the ages of your kids, I'd recommend you also spend a few days in Williamsburg. It's just a few hours further south but really worthwhile if you have the time. We stayed at American Heritage campground there. We have a similar sized MH to you.