I can offer support but no suggestions. I am in hte same boat. Married for long enough that the ex has decided I'm the devil and is working to convince the children of this as well. They know better, but her leaps of logic are not as obvious to a child as they would be to an adult who had more understanding of the way the rest of the world works.
Best I can say most times is "congradulations, you've managed to give a snow job to a 14 year old and a couple of neighbor friends who have to live next to you and don't really want to hear the WHOLE story."... but of course I don't say it, I just think it.