My opinion is it should be based on the age of the kids. Your two older ones I would tell. They need to know why the family is being split up. The younger one could get a lighter version. But lets face it the kids will talk to each other. So I would sit them down (without the wife..she will try to blame or water it down) and then ask them if they have any questions. You don't have to be graphic but they deserve to know why their world is going to change forever.
