Telling the kids can be difficult. My kids are a little older,(12 and 14 at the time). I let W tell them while I sat there to intervene if she blamed me or made it sound mutual. I didn't intervene...she was fair with her delivery. We waited until after the kids were done with finals, but it was still a couple of weeks before she moved out. I'm not sure the timing would have ever been good.
I think my advice on that would be wait till its almost time, but still with enough time for them to absorb the idea of it. I'm so sorry you are having to go through this. It is HARD!!
