Let your heart be as heavy as you like but don't let the children know. This may sound obvious, but make it new and exciting for them. Let them think - by the power of suggestion - that they have some choice in the new house, the new school. Make sure they know they will have familiar things around. Talk about it a lot. And then some more. Try and draw parallels of friends who have moved into/ out of the area - let the children know they aren't the only ones that do this. Sell the new life really well. When you see they are ok, it will make it easier for you to begin to feel happy with the move too. PM me if you like. I'm not clergy but happy to chat. All I can say is that positivity really works. It will be a wrench but you will all grow from it. Good luck!
Your children are at an age when they are really resilient and will sail through the move (much more easily than you will). Starting school is actually a good time to move somewhere new because everyone is forming those friendship groups and you will get to chat to all the other new mums in the playground. My DDs talk fondly about friends that we've moved away from but the places matter much less. I'm sure you will given a warm welcome in the new place and it will be a happy time for your family. Good luck from me too.