Then you need the ex's permission, and will likely have to go to court to duke it out if he decides he doesn't want to give it.Just out of curiosity, what if the divorce decree does say you need the ex's permission?
If ex will not give permission for the move, you'll need to file a motion with the court. You'll need to be able to prove to the court that the move is in your childrens' best interests. Since ex will have an attorney, it would really be best if you hire onw also. If you just can't afford to, you need to get a consult with one and read up on your state's laws and court rules before you file.