I think it is good for the kids that parents are able to get along. No matter the problems in a relationship or whether an OM or OW is involved. My xh and I used to spend holidays and birthdays as a family even after he left. This was when he had first OW (I was in the dark on this one for a long time) but now that he is living with his new gf, we don't get together at all. I have to admit it is my fault though. I want nothing to do with them. He once told me no matter if he was with someone or not he wanted to remain best friends. It worked until I got a boyfriend. Now he stays angry with me. It is like he doesn't want me but he doesn't want anyone else to have me either. Or maybe he sees that I am happier now than I was with him. I don't know. I just live day to day for me...and my girls.
Do you think your xw has a fear the kids will have more fun with you? Maybe that you will take them away from her? When you weren't talking to them much she had control, now she is losing that control...or thinks she is.