I always twitch when my kids spend time with STBXW when they are supposed to be with me. I don't want them spending a minute more with her than they are legally obligated to. That said, in my case it is borne out of an insecurity that they like her more than me, and a fear that she will take them away from me. What is driving you?
I wish you a very happy (belated) birthday, and many more in good health.