We did it when our children were 8 and 10. We both come from cornwall and had moved away at 18. So we had parents here (though to be honest had zero help from them!) who we were able to help look after as they declined.
All our London friends warned our children would be bored. They weren't. We live between two villages, and all it meant was that at 17, in contrast to their city peers they cracked on and learned to drive.
I had to do a lot of driving - between hobbies and commitments and school, so taht was a bit of a nuisance.
I agree education can be a problem. The issue is aspiration. It's low. Or was when we moved. We came from an area of high expectations, and fortunately those stayed with our children. We too had high expectations and never let them forget it! They remained state educated and ended up at Durham and Cambridge respectively. So no harm done. But yes, I do admit education can be hit or miss.
Health care too is a bit iffy. There's a sense of being the end of the line. If I'm honest I worry about being old here.
Culturally London friends felt we were going into a black hole. Again, not true. Plenty of theatre happens here in the summer in particular, and I think we make more effort to see things because we don't take it for granted.
Regarding fitting in, I really think that's up to the individual to get involved. Plenty of opportunities to get stuck in, and locals appreciate that. Remember locals aren't just people born here, they're people like us who moved back, or moved because we fancied it.
My children are now in their late twenties and ironically back in London. But they love coming back and consider themselves Cornish. There's a real Cornish community in London - we seem to find each other!
I live a rich life here and have no regrets. I walk daily with my dog in world class scenery, I spent the summer in the water, I play my favourite sport twice a week, have a big garden and bigger house than I could afford in London, and lots of lovely people as my friends
Why not consider somewhere like Falmouth? I do think the south coast is nicer than the north (where many communities are hollowed out by second homes). It's a problem too on the south coast, but I do think the north is worse. Ot Looe - which is close by train to Plymouth and therefore the rest of the country