Yup it's sad and it will be even sadder for their Dad when the kids don't want to go because they are afraid of missing out with their friends. That time will come.
You're doing the right thing in making sure that the kids spend time with him. How could you live with yourself if you didn't do this? Having their Dad around even for a couple of hours is better than nothing. He's still missing out no matter how you cut it.
Don't worry about what you can't control and how he parents when they are with him. I do totally get it but you'll just be making yourself crazy with that one.
