Yes, but the problem is that whenever they have a disagreement, or she doesn't get her own way, or she thinks that they are having a good time with someone else, she involves the kids and upsets them. I know, as I have been there with DSis, when the ex-P has called the kids and deliberately said things to upset them.
Last Xmas, (they do alternate Xmas Days) she rang up at 9am on Xmas morning and cried and wailed at the DC's down the phone as she was missing them so much. FFS they were going back to her at 6pm that night, and had only been dropped off at 6pm Xmas Eve. They have been divorced for 7 years and alternate Xmas days has been in place every year, but the first year they are DSis's then there is this massive scene.
DSis met her DP just before the previous Xmas which was the ex-P's Xmas day year, but did not meet the DC's for some time until they both knew it was a serious relationship. And she met the ex-P before meeting the DC's at the ex-P's request.
Another time, we were all away, his agreed contact weekend, first day of a family weekend trip camping (Me, DH, our DS3, DSis, her DP and his 2 DC's) and the ex-P called and told the DC's that the family dog had died. Weekend ruined, DC's distraught and there was no need for it. She could have waited for 2 sodding days for them to get home.
But then, when it suits her, like when she wants to go out and it is her weekend, expects everyone to drop their plans and have the DC's because "She deserves a break sometimes." Even though he does most of the holiday care (He works from home and can set his own hours) and 3 school pick ups a week to save her childcare costs.
The poor DC's are only 9 and 11 yo, and her DP really doesn't want to rock the boat or make a fuss that would cause an all out war which would just mean more damage to the DC's as he knows that she would involve the DC's and he does not want to be seen to bad mouth her, as she is still the DC's mum. So frustrating.