It's very hard to process that today is the 15th anniversary of 9/11. 15 years ago I was a teacher but I wasn't yet a Mom or an author - the two things that have changed me the most as a person. The students who were in my class that day now 23 years old. They have finished elementary school, and middle school, and high school, and college, and are now out in the world, hopefully doing something amazing. I give you this perspective because while 15 years doesn't sound that long ago, in many ways it was another lifetime. Explaining those events to today's children is explaining history. Thankfully was have authors who found a way to tell the story to different age groups.
For Younger Children
14 Cows for America is a picture book that features a true story about a Kenyan tribe that gifted 14 cows to America in order to help in our time of need. There are some strong images so parents should read it first. You can see more about the true story of these cows by reading this CNN article.
For Middle Graders
In nine, ten, we are introduced to a number of kids who are all at the airport at the same time. They notice each other, but do not meet. We follow these characters for the next two days, experiencing their lives and family relationships. Each one comes close to the tragedy, but does not experience the tragedy directly. They are all changed by the events and at the end of the book the kids are again at the same place at the same time, but this time instead of ignoring each other, they bring us a message of hope.
There are a number of other new books that have been written on this topic which I have personally read. For other suggestions, take a look at this article from the NY Times.
As a teacher of third graders and a mother of an 11 and 13 yo, I am very glad to have these books that tell a tough story while keeping the age and experience of the readers in mind.