Thank you for this post and sorry for your losses. In our society, death and grief are not spoken about enough, and so people don't know how to support others when a tragedy happens. This often makes dealing with a loss even harder, especially an out-of-order death one cannot rationalise. Your title does not do the post justice though. I flinched a little when I saw it as I have spent the past year supporting a family who have lost one of their young in a car crash (she was the pedestrian), and my daughters who lost their life-long friend and housemate. I have learned a lot in that year and wish I had done that learning before I needed it. My heart goes out to all parents who had to endure the loss of a child. I cannot imagine anything worse.
There are many things that go unspoken during life, that list is long and vast but death is towards the top. There are also many layers of death and each type is felt differently by each person in proximity to the death. There is an echo effect that ripples outward from a death and a birth.
Losing anyone is hard at some point, yes a child is unlike any other loss. There is no way to prepare for that type of loss. Nothing that can be said after to ease the tear felt in one's existence. No way to ever forget. It is the one time I truly thought that there may be some type of needed continued existence of lobotomy experiments, to master the selective removal of certain memories.
My heart goes out to those you speak of.