It is a sobering and sad day. It is one of those days where we generation remember exactly where we were when we heard about it.
As Mik said, it is important not to forget, but CatsEye is right, time goes on.
There are no "children" today who were alive when 9/11 happened as it was 19 years ago.
It is like any "defining" event in US (or world history). How many people remember the end of the World War 1? Less and less people remember the atomic bomb to end the World War 2. etc.