My daughter was 6 when 9/11 happened. We were glued to the TV and they had a prayer service at her school that day, so she was aware of what was happening.
That night as I was helping her take her bath we had this conversation.
Why would someone do that, mom?
Well, someone wanted to hurt a lot of people.
She had questions about the logistics. She thought one plane hit both towers and couldn’t get her brain around that. So I told her it was two planes each hitting a tower.
She thought about it all for a few minutes, then she said,
The devil was there today, wasn’t he mom?
I said, yes, honey, the devil was there today. But Jesus was there, too. He took a lot of people into heaven today. And he was there in all the people who were helping each other, in the people who ran in to help, in the strangers who did kind things to help other strangers. Jesus was there.
I would just give them as much information as they want and need, using their questions as a guide. Just like with sex or any other topic, their questions will change as they get older and seek more detailed answers.