I caught my 12 year old watching the Today Show this morning after I got out of the shower, so she's completely caught up on the situation (grrrr). She and my other daughters have spring break this week, so I suppose I would rather they find out at home than from their classmates.
I've made sure that she knows that the people who were injured are being helped and taken care of, and anyone still missing is being searched for. She in turn told me that Google is helping people too.
Here's the Google help link:
http://google.org/personfinder/2013-boston-explosions
As for my younger daughters, I'm still trying to shelter them until more information is known but I'm going to have to tell them something before they go back to school on Monday. I just don't want to give them the vague, "We don't know much" version because that causes my youngest daughter to feel much higher anxiety than she might otherwise. She's my worry wart.
So. What I do is talk to them (again) about safety in public. I talk to them about telling an adult if they see something out of the ordinary, and since they know what their surroundings normally look like then when something is out of place they should say something. If they feel uncomfortable about something, they should tell a grown up and explain why if they can.
We also talk about how important it is to do what emergency personnel tell us, but also how important it is to help others when the danger is over. We talk about what to do in an emergency and what to do if we get separated in an emergency.
We have these talks anyway, so it's not out of the ordinary to the girls to have them. They just figure it's "reminder time."