I like the way our school handles these things.
When something happens during the day (Sandy Hook & Boston), there is no mention of it, an email goes out to the parents explaining how the teachers will answer questions the following day. The approach is generally to answer questions briefly and honestly, and to assure the kids that they are safe.
Sadly, our school staff have had to deal with a number of events in the last few years. Events that happen in the evening or that must be told to the students about members of the school community, teachers meet at the school at 7 am with a crisis team to discuss their approach to talking to the students. It's always been done matter of factly, honestly, and briefly, with a focus on not letting misinformation spread. In one recent event, the kindergarten students were not told, and the parents were asked to handle it as they saw fit. This was clearly communicated to all parents, and the communication invited parents to discuss sensitivities with teachers before the start of school.
