That can be a very sticky thing when going out of country. Our sons has to leave permission for his wife (they are married) to leave the county. He is in the Navy and usually has a check list, she travel with the kids to Japan when he ships out.
An old room mate of mine had sole custody og his daughter, but he could not take his daughter to Canada without his x"s permission. My X brother in law got in trouble to taking his kids out of the COUNTY. A mad X can make thing very very bad. I would get your ducks in a row before trying to take them out of country.