Are you in possession of full custody of your children and your ex abducted them and went abroad, to a country where your rights cannot be enforced?
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There are cases of custody awarded to one partner, when the other reacts by kidnapping the children and fleeing them off abroad, where your legal rights cannot automatically be enforced. This is a classic case where a private investigation agency may be your only realistic answer. According to the Law, child repatriation can only be enforced through the Hague and the European Conventions.