I visited the NYC Police Museum a few years ago when my son was about 7 years old. He was very interested in the 9/11 exhibit there, but was tough talking with him about it.
Our thoughts are with all that were lost 12 years ago.
That museum is a great one to visit – the exhibits are well done and it is located in the Old Slip police station near the South Street Seaport. Sadly, it has been closed since Hurricane Sandy – hopefully it will open again soon.