Dr. Bob Barnes says, "You need to not get in those little verbal battles and games that happen between ex spouses regarding visitation. Do the best you can to cooperate. Whether your ex cooperates with you or not is his or her decision. You need to do the best you can for your children's sake, and you need to not compete with these visitation times. Be happy for your children when they come back happy, and do not make them feel guilty about good things that have happened in their lives. You need to be mature and be glad for your children, even though what your ex is doing just grates on your nerves.
"Strive to do the best you can. Every time you make a mistake, when you raise your voice at your children and when you say something you wish you hadn't said, you need to apologize to your children and to your Lord. The beauty is you're going to be able to start over tomorrow."
Remember that the relationship between you and your former spouse has changed. You are no longer working on a marriage but you are now two people parenting the same children in separate households. Your focus should be on your own parenting skills and issues.
"Serve wholeheartedly, as if you were serving the Lord, not men" (Ephesians 6:7).