I'm sorry that he's acting the way he is...but he's the one that has to figure out how to rebuild the bridge between himself and the children. Your children are old enough to determine what they want to do with respect to any type of contact w/their father.
I would suggest that you be there for them, listen to them, but don't attempt to fix the situation between them and their father.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
