My son is six years old, and when I asked him if he knew what “9/11″ referred to, he didn’t know. I simply told him that very bad people flew airplanes into two buildings and killed about 3,000 people. He understood that it was very serious, but he didn’t ask much more, so I left it at that.
I found a video that I think I may show him next year. If you have a child age seven or so or older, it could be worthwhile. I think it is thoughtfully and sensitively done.