Hi wm, have you talked to the school about how they are handling this, and what support they have?
They may not know (lots don't) but there is a lot of support out there for the school, not just in the form of counsellors etc but behind the scenes help, e.g. literature that could give to the parents (about the signs of grief/anxiety in kids at different ages) or used in the classroom, Emergency Planning staff from the district council who can help put the school in touch with other supportive bodies, or plan how to handle similar situations, other people who could help support the staff, including teachers who have experienced similar situations and can help advise staff on what to expect in the days, weeks, months and even years after a disaster. Its not all psycho-social stuff, there are practical tips too.
There are lots of 'lessons learnt' from other schools that have suffered bereavement too, about how they handled everything from the initial phone call and telling the kids, through to impact on exams etc much later in the year, anniversaries and memorials.
I firmly believe that schools can give a lot of stability to communities, who have suffered a disaster or bereavement like this, but the teachers have so much to do already, and are often bereaved themselves, so having support in place and knowing how to access it when you need it is important.
Kids pick up on the littlest things, while there is no easy way to deal with the situation there are some little things that might make each day easier for staff, pupils, and the wider community.
Heart goes out to you and DS; when I get home I'll dig out some links and references that might help you understand how children of his age grieve or are affected by grief around them. From memory it can be things like reverting to bedwetting, not liking to be by themselves or have loved ones leave, misbehaving... and doesn't have to happen now - could be weeks later, you just have to be aware that it might be connected. Your doing the right thing by talking to him and keeping the channels open for his questions.
Might be worth asking his teacher how they introduce death at school - its in the curriculum now I think, but they often talk about Pets first not people, and might choose to use certain words/ books etc, these are often available for you to borrow just to see what the school is doing. Hope this has helped a bit - am dredging my brain now ? sorry to go on - this was my dissertation topic!