When my son and DiL told me they were moving two hundred miles away as my sons job was moving there, my first feeling was that I had been kicked in the stomach. Then, they lived less than five miles from me and I saw them a lot.
Then I went to use their bathroom and stood in there looking into the mirror counselling myself. Yes, I would not be able to see them so often, but probably for longer periods when I did.
Yes, they would be able to get a nicer house, probably with lower mortgage in a lovely area
Yes, their future lives were far more important than any feelings I had
Yes, I should be happy for them and support them.
So, I went back downstairs to encourage them with this move.
That was seven years ago - has worked out wonderfully for them (and I have my own room, en-suite) in their beautiful house there. Since then, I have also moved away from that areas, so even if they had not moved I would still be just as far from them.
As for g.children, well usually as most youngsters enter their teens they draw back away from those extended family relationships (quite correctly and normal - part of growing up).
My sister in law had an extremely close relationship with one of her g.sons. He did have some behavior problems and she was the best one to deal with them. When she moved away and was not able to continue seeing him daily he actually cried at school about that (unusual for a 10-year old lad_. She was distraught and, when I told her that within the following five years he would be wanting less time with her in any case - she replied that He would ALWAYS need her. He is now fifteen, and she moans that every time (it was weekly before Lockdown), she visits his home he hardly even notices her being there, as he is busy on his screens!!!