My guess is that your feelings are tied to his still. That's not detached, right? When he changes, it brings up feelings in you. Don't worry, that's how it works until you are detached. Just note that you are not as detached as you might like to be and work on it.
As for the rest, I would be encouraging when he does things with the kids. I am in my own situation and I highly recommend it for the sake of the kids. As was noted, I wouldn't say you were happy with him for it, but rather you might mention you notice the kids are happier with him spending more time with them. I think that would be enough to encourage him without your involvement. If the opportunity comes up. I wouldn't force it either as he learns to be a parent to them. It'll happen gradually with fits and starts, so don't be discouraged.
Peace, AJ
"Our lives begin to end the day we become silent about things that matter" MLK Put the glass down... "Yesterday I was clever so I wanted to change the world Today I am wise, so I am changing myself."
