Hi Nick,
As you can imagine, this is one very emotive subject and one that many have anguished over. I don't think there's any easy solution and the usual is to recommend other ways of keeping in touch, which you've already listed. The Internet, webcams and cheap phone calls do offer a good deal of solice as they are real time and interactive but, when you're talking about future grandchildren etc. it's a different story. I'm sorry I can't offer any magical answer, but just wanted to commiserate with you on your predicament. I hope someone can tell you how they are managing to cope, but, obviously, the best outcome would be to encourage both your son and daughter to work towards emigrating, but, as we all know, it's not always that easy.
Good luck.
