I was 11 at the time. Really, the most I felt was annoyance that every single TV channel was broadcasting 9/11 reports, and so I had to either watch that or do something else.
In all fairness, I'm not American, have no immediate family in America and none whatsoever in New York, so I saw no reason to get emotionally invested. I remember my mother would watch (and still does, for that matter) the World News pretty much every night, so in my 11 year old mind, stuff getting blown up somewhere overseas was nothing new.