The question is: what do I tell the kids if she decides to move out? What do I do if she tells them ahead of time without me?
If your W moves out, I'd suggest to tell them something like this, "Sometimes adults don't get along just like kids sometimes don't get along, but adults don't get over it as quickly as kids. That's why we need to be a part for now." They are young, so try to protect them as much as possible and not overwhelm them with too much.
The second question, you should address your concerns with your W about telling them. Right now, it is up to you to shield them from this mess. Don't be afraid to discuss it with her. It isn't going to make or break your sitch. I know easier said than done. Your kids need you to step up to the plate. You are their hope.
Me:45 ExW:48 M:04/97 3 Bombs & 2 ReCons 1st BD 11/10 D Finalized 4/20 D-16 S-14 Going in one more round when you don't think you can. That's what makes all the difference in life.~Rocky Balboa