Hello, Nannie4nanna, and welcome.
My brother is in Australia, although neither of my children have emigrated, yet at least.
You have my sympathy, as I'm sure it must be very difficult to have a child so far away, but the world is smaller than it's ever been. Maybe visits can't happen often, but Skype/Facetime calls can be the next best thing.
I sometimes wish that my children lived closer (they are both over 120 miles away in different directions, which means that visits have to be planned, and take up a day, rather than being able to see them for an hour or so as would be easy if they lived nearby), but in the end we all have to find ways to make the best of what we've got.
My brother speaks to my mum every week at a prearranged time, so it always happens, and she has seen her grandchildren grow up that way, in between visits.
Chin up. I know it must be very difficult, but you can take comfort in the fact that your son and your grandchildren will have a lovely lifestyle over there, I'm sure.