to tell you about parking. Our plan of action as a family is that whenever we go visit a large city, we use public transit to avoid issues with parking/traffic. When we were there, I did notice people in cars: rush hour was basically a gridlock. From what I remember, there is no designated parking for the science museum. By the way, the science museum has the highest attendance of all Smithsonian museums. So like a good boy scout, be prepared!
Another thing I want to mention is that I did get timed tickets ahead of time for the Holocaust museum. We spent minimal time in there at 3 hours, and still missed some. There was a holocaust survivor/author from Holland in the gift shop. I purchased a book and he signed it. Even at the early time late May/early June we went, there were LOTS of people in there.
From what I recall, they do NOT allow cameras or video taping in there (and regardless of the rules, people still do it-they have a no rules apply card...I'm still trying to figure out how to get one of those!). If you are planning to go here, visit the museum's website to get more information.