An excellent museum for history and science aficionados which should also appeal to the masses. It gives a very comprehensive view on flight evolution. It successfully vulgarizes science thanks to hands-on interactions and detailed models while keeping enough scientific details for the science nerds (like me :-D). Even though it can feel a little bit dated at times, as technology evolves quite fast, it'is still worth going and you should plan several hours to tour it (at least half a day). Tip: there's a McDonald's inside, much cheaper than other options around. It makes the museum a great place to either start the afternoon or stay the full day.
Fun place to visit in DC if you have an interest in history. Personally enjoyed it just because of my interest in space and flight. Has a lot to offer when you visit. If you plan on seeing everything it has then I'd suggest coming somewhat early when it opens. Tends to be quite crowded in the middle of the day and afternoon. Had plenty of places to rest and good restroom access. Probably not a good place to come for peace and quiet though as it can be loud with all the children running around. Has plenty of activities for children when visiting. It is all handicap accessible too. Would recommend if you visit the DC area.
Science is real folks. Free admission. Customary security checkpoint right by the doors, so be prepared to have your items scanned through. Gift shop is huge, not cheap, but you can and should find something to mark the occasion of visiting. Some amazing exhibits and some are quite big! This is where you bring your kids interested in anything mechanical. They will love seeing the amazing array of aerospace displays. I spent the time walking around by myself and had an amazing time just marveling at human ingenuity. Weekdays aren't too crowded, just FYI.
My husband is kind of a rocket scientist ("No, I tell the rocket scientists where to go," he says), so I'm at the Air and Space Museum quite often because that's always where people want us to take them when they visit. It's a pretty neat place--lots of awesome historical pieces, cool videos, fun trivia, etc. I really enjoy going, and I look forward to taking children there when that time comes. Oh, and the best thing about the Smithsonian--it's free!
It's important to remember that the Smithsonian Air and Space Museum is truly a National Treasure. A wonderful place to take the kids whether it's cold outside or hot. My only issue is that there's a McDonald's connected to the museum period otherwise it's an absolutely wonderful place to take friends family and kids. Plus it's within walking distance to seven or eight other museums and plenty of other better places to eat