JB
Have you read Divorce Remedy or Divorce Busting?
You have to Act as if. Act As If you know that she is going to say yes. She is going to say "What a great idea!"
I would approach it with "Look, I think the kids could benefit seeing us together as a family. It's been hard on them and I think we both want to put them first, actually I know we do. So how about we try a family night? We'll go to dinner and maybe some ice cream. We won't talk about anything except them. We'll make them the focus. We'll ask them a million questions--make them the center of our attention like they deserve. If you are ok with this and I'm ok with this and this first family night is a success we'll try another one, maybe roller skating or bowling or a movie, whatever. But this is for them, not for us to talk about semantics or the divorce. This is for talking about and to them about them, only."
Go for her guts JB.
Also make it clear, you are already going to do this, with or without her. Even if she says NO, family night is still going to happen. My gut tells me, she'll change her mind when she sees how much fun you and your kids are having.
Do it JB.