OR - just accept that they are going to meet her and that you really can't prevent this. Yes, them meeting her before you all divorce carries the risk that they'll figure out he was cheating and may hurt their image of their father - but that's his problem to deal with. And truthfully, by August, if they already know you're divorcing, they may not even connect the dots.
Did you ever see the movie She-Devil with Rosanne Barr? For some reason, I am envisioning the scene where the kids go to stay with her ex and his mistress, Meryl Streep - too too funny.
