We have not told our boys yet, as we are waiting until we know for sure. But luckily our eldest is very keen to see new places and learn new things...so fingers crossed he will be as excited as us when the day comes.
I think maybe, get them involved in the process, with showing them things to do in the area you are going to live, and what they can do in school, sport-wise for example. Try and make it as interesting and exciting as possible for them. Good Luck! I will let you know how we get on when the time comes (if all goes well).