I can't imagine seeing a healthy person die. I'm so sorry. It sounds like you are of faith, there is often some console and inspiring verse there (no matter which faith.) If not, I have a lot of friends that turn to art, literature and music to find peace in time of grief.
Even just for the loss of pets there are amazing books (cat heaven and dog heaven) there MUST be something for children that experience this sort of thing. Hoping for peace and comfort for them - AND you!