Well, if your ex is with the children visiting in another country, the first question that I would have is, is that country a member of the Hague Convention. It’s the Hague Convention on International Child Abduction. If they’re in a country where that is a party to that convention, then if your spouse doesn’t return, you can petition under the convention for the return of the children to the US.
If they’re in a country that’s not a party to the Hague Convention, then it’s going to be more difficult. There are things you can do though, such as, obtain a court order from the Minnesota courts that declares that Minnesota is the children’s home state and that the children must be returned to Minnesota. You can then take that Minnesota court order potentially to the other country to have it enforced there.