We took our kids years back to the mall for the 4th. They were about the same age as yours. They are in their 20’s now and they still talk about that day. It was a fabulous experience. Yes it will be crowded; yes it will be hot/humid, still very worth it. We stayed outside the city in Millersville and took the Metro in early in the morning and stayed on the Mall all day. There is obviously plenty to do to stay busy. We staked out a claim in front of the Lincoln Memorial very early before the crowds started to build. We played cards, took naps, ate etc… until the show started. After we briskly walked about 6 blocks away to reach a Metro station that we thought wouldn’t be as crowded. It worked out well, we made the second train that showed and had a nice ride back to Millersville. We did make a nice relaxing day for the 5th, sat around camp. It is an experience that you must do for your kids.