If you want to stay in Washington, Hard Rock is fun for kids, but many will say it is overrated as well. My kids like it nonetheless.
CapCity Brewery is good too as a pp said and we stumbled across Gordon Biersch, which is a brewery and was VERY nice! It wasn't themed-like for kids, but the food and service were fantastic! My kids really liked it and it was nice cool place to sit and enjoy our meal and a few light summer beers for the adults!
As another pp mentioned, Tyson's Corner Rainforest IS closed and I don't know how far the one in Maryland is. If you do end up going, my suggestion would be to share meals, even kids' meals, as the portions are very large.
Our favorite to share are the pita quesadillas. They are consistently good.