It feels sad because it goes against human instinct. In hunter gatherer groups people generally didn’t leave, and when they did leave (because the band got too big) I think they generally fractured voluntarily along bilateral sentiment lines (because why wouldn’t they, what are such sentiments for after all).

Which isn’t to say that we should prevent it in our own lives today, because we do live in a society. But I think it’s worth reflecting on how the structure of today’s society prevents the formation of larger kin groups.

To the child it feels less sad because the parent is basically a sort of captor, who is implicitly forced to mold the child to the behaviors required by society and the child generally holds some level of grudge, often subconscious, against the parent for the actions that are taken to do this to them (such as forcing them to live inside a box and suppress a large variety of natural instincts from early childhood on, among other things).

My honest answer is pray for them twice a day and do call them everyday just to tell them you are there for them and in you they will have a constant friend, and supporter. Because young people go through a lot of sadness too when they are all alone in the world. I personally converse to my parents like I am / or they are writing a diary. It has worked well. We haven't lost touch and we pick up right away when we meet. But physical loss is really hurting. Prayer will definitely mellow down the mourning and will give positivity to the whole situation.