This just makes my blood boil....kids can be pretty black and white and unfeeling toward other children but in this instance this is purely a reflection of what they've heard from their JW parents.
It seems to me, it's this kind of behavior that demonstrates that JW's are just another religion with a "form" of godly devotion but proving false to it's power. They are more interested in feeling morally superior and extra virtuous over your ex and daughter, than they are in being kind and "Christ like". Who could be that cold to a little child?
I wouldn't be surprised of this puts your ex one step closer to the exit door, for good.