Brit here, but at the time I was 9 years old and living in Berlin. My mother was driving me from school to a karate club, and she turned on the car radio to BBC World Service to listen to the news. We were both pretty shocked, but neither of us were massively upset IIRC, I mean, not compared to any other sad story appearing on the news. Pretty much all I knew about the World Trade Centre is that they were in NYC and they were two of the tallest buildings in the world (I was quite a nerdy child...), but I knew nothing about terrorism or Islamic fundamentalism or anything like that; I was just amazed that somebody had thought of crashing planes into skyscrapers like that. But obviously my mother would have known the political and economic impact of the attacks better than I did at the time.

The next few weeks were a very weird time. Lots of two-minute silences at school, lots of events and festivals being cancelled, etc. etc...And pretty much the only news story every single day was the Twin Tower attacks, reported as if it was a Breaking News story even weeks after the event. For BBC World, every day was Groundhog Day.

I also remember a week later, when I went to karate class again, all the kids were talking about how great it was that Osama Bin Laden had destroyed the World Trade Centre and killed all the people inside. Unfortunately I don't remember in more detail how they justified their opinions, but most of the people there were from working-class Turkish immigrant backgrounds and were barely older than I was, and I imagine they were just parrotting what their parents were saying at the time. Needless to say, I did not attempt to counter their opinions with my own.

Funnily enough, the 7/7 bombings were much less of a shock, despite having been back in London at the time. But by that time, various other Al-Qaeda bombings had already occurred in various other European cities and everyone had got used to the threat of terrorist attacks, and so a terrorist attack in London seemed much less of a surprise than it did when 9/11 occurred. Being significantly older at the time and more knowledgeable about Al-Qaeda and the Afghanistan/Iraq Wars also helped.