I will read the answers to your question with interest, because we are in the same position. I am the primary breadwinner in our family, and was told 2 weeks ago that either we will relocate, or I will be laid off. I, too, am worried about what it will do to my kids. My husband and I can see some huge upsides to moving (we don't love the town we live in now, and moving will allow my husband to have a better job too, actually). But of course, the kids just started their school year, and are involved in ballet and different school activities. I hate to pick up and move them mid-year.
But, moving mid-year is better than being homeless, which is our other choice. The kids aren't happy about leaving their friends, but the deal I made with my older daughter is that she can go on Facebook every day (supervised, obviously) to chat with her friends, and we have Skype so she can also have video chats with her friends. So she is okay with that.
The other thing we have been able to do (we have to move about 3 hours' drive from here) is take the kids house-hunting with us. Granted, they haven't come with us every time, but because they saw the kinds of houses and neighborhoods we were looking at, they were excited. They enjoyed deciding which room would be whose, which side of the bathroom they would each put their things in, etc. We have been watching House Hunters on HGTV and watching how other families choose their new homes, and that the kids look happy in the new house, etc. Basically just showing them in so many ways that moving will be okay.
But yeah, no matter what, pulling the kids out of school and having them start somewhere else mid-year is hard. You're not alone! :-/