I agree with Jersey Girl and I think you may be unintentionally putting your issues about your ex on to your children.
You are doing them no favors by letting a 9 year old choose whether or not to visit their father. Your children will resent you as an adult if you badmouth him or hinder their relationship.
Trust me, I know it is hard, after everything that has happened, and even when he is being a jerk now. But you have to rise above that, not always, just when it concerns the children.