And I do not think its over with even though Usama BL is dead.
When Mr W and the Womb Raider get older, I will tell them that evil exists in the world and massacres are part of our horrible past in all human societies - and that everywhere and every time we have to be on the look out for it in all its forms - and then confront it when it is found.
Once they understand the general concept, then we can talk about 9/11 as being just another, extreme (modern) manifestation of it.
Other modern examples are the doomsday cults in Japan, the Jonestown massacre in the 70s, the Boer concentration camps, the Armenian massacre, the the Rwanda massacre, the Holodomor, and the Holocaust.
Your explanation is missing something important. 9/11 was not an isolated attack but part of a jihad. My children will learn what that word means.
