Here's my experience (not opinion, experience):
We moved over to France nearly 10 years ago, to renovate an old barn (not finished yet).
Have tried to learn the language and are reasonably integrated with French, English,Scottish and American friends - probably a more diverse set of anglophones than we had in the UK. However friendships in any other language than your own take so much time to develop, which is often the reason English people socialise with English people, it's much easier. Unfortunately often the only thing you may have in common with them is the language - and of course there is a much smaller friendship pool!
We both have grown up children from first marriages.
My husband's children visit us twice a year, with his toddler granddaughter. He doesn't much like going back to the UK, so this suits him well. We love the little girl and make sure we have facetime (although tbh she's too young at the moment to take much notice). I also made a little book for her with lots of photos of us - I'll do that every year.
My first grandchild was born in December - my daughter's who has not shown much interest in coming over. I'm over every other month to see them and spend a week at her house - fortunately I get on well with my son-in-law - I did spend 2 weeks with them post natal, and was so lucky to be able to help. I think my relationship with my daughter has improved as she was quite resentful of me going (she was 22 at the time). My son and his wife keep promising to come over, but their life gets in the way. So I spend some time with them on my bimonthly trips. I have 3 really good UK friends that I will try to see. They are very old friends and you can't really make 'new' old friends.
So some advice based on my experience:
I agree with people that it's best to keep some property in the UK (you can rent it out). We didn't do that. If we do come back we won't be able to afford as lovely a place as we have now. But then we have it now, and love it.
Try to find a home close to public transport - one of my criteria was to be within an hour of TGV and an airport. At the moment I fly over but will be able to train as well. I have even taken to bus (3 buses ) when there was a strike, but will only do that if it's the only way to get back.
Learn the language - the admin and beaurocracy are so onerous - and do tons of research about the laws of the country you are coming to. The number of people that don't know about registering their car, changing their license, paying taxes etc etc , getting into the health care system and thus get into trouble is worrying. I have had English friends with no french, got old and I'll, it's so isolating.
It is you that has to make the effort to maintain your relationship with your children, but it is easier to do nowadays . And as people said, they will.
I could go on, and will probably think of more later. If you want any other info/experience message me