Thankfully I haven't had to bury a child, but that doesn't mean that I haven't been affected.
I lost my oldest brother to a drunk driver when I was 9. I watched as my parents had to deal with his death and then my other brother going off to the army during the Vietnam war. Right through high school I lost friends to different deaths.
Needless to say, by the time I had my two sons there was no way I could live in the bubble of "immortality" that you mentioned. Then in 99 we had the May from hell where we lost a family member a week for the whole month - including my other brother who was hit by lightning. This brother was a huge part of my son's lives, and so they also lost the ability to believe that it could never happen to them.
Most of you know I lost my parents within a year of each other. Then this year, my son Brian lost his best friend and another friend to a drunk diver. I have tried to be there for the mothers of the boys and for Brian, but I don't remember any of them ever saying they felt alone.
One thing I will say, is that once you have lived through this, you can spot the people who have never lost anyone close to them. These are the people who expect you to "get over it," and don't understand why you are still "sad" two months later. I saw this happen with Mum and Dad, and to the mothers of the boys who were killed in January.