Hi, I'd like to help you with your question.
This is a difficult part of custody arrangements for parents. Each person is going to want to parent the way they see fit. If you were still together with your ex wife, you both would be most likely arguing about what was appropriate and you would work it out in some agreeable way. But as it is, you are divorced, which makes this very difficult because now it has become a power struggle with the kids in the middle.
It is a good idea if you and your ex wife would sit down together, just the two of you, and find a compromise. Tell your ex wife that you want to do what is best for the kids and that both of you should be putting the children's well being first. Then find a compromise. The final agreement should not be one sided either. If your children want to ask you questions, for instance, then there should be an agreed upon limit to your answer. For example, if your daughter asks why you live so far away, you respond with what you said about mommy and daddy living apart because they aren't married anymore. Follow up with telling her how much you both love her and care about her. Then let it go. The idea here is that you are able to answer the question, but you appease your ex by limiting the information.
If your ex will not agree to compromise, then suggest short term counseling to work out the issue. It doesn't need to be with a therapist. It can be with a pastor, mediator or a neutral family friend. Someone whom you both believe can be neutral.
But if neither of these work, then you may have to resort to legal means to get your right to see your children. You want to avoid this as much as possible to spare your children and try to keep a civilized relationship with your ex, but if she refuses to work with you, seeing the children takes priority over your relationship with your ex.
Here are some resources to help you find more solutions:
Surviving Divorce and Custody Issues: The Single Father's Guide by Anne P. Mitchell
Building a Parenting Agreement That Works: Child Custody Agreements Step by Step by Mimi Lyster Zemmelman
Stop Fighting Over The Kids: Resolving Day-to-Day Custody Conflict in Divorce Situations (Mike Mastracci's Divorce Without Dishonor) by Mike Mastracci
You can find these books on Amazon.com or your local library may have them for you.
I hope this has helped,Kate