Be supportive of them. Don't pressure them into forgetting, because forgetting is the worst you can try to do. You can never really forget the past, but instead, you can look the future and see that past occurrence as an opportunity to learn and be ready for what's in store. It worked for me, when someone I loved committed suicide. I can never forget it, but I don't try to burden myself with it; instead, I just try to see it as a sad occassion in life that I didn't have control of. I don't blame myself or anyone around me. Everyone has the choice to decide their fates, just as I have and she had. So just sit down, tell them to look forward to the future. If you think pessimistically, it will only get worse.