The Boston Globe has a brief article about the problems parents face retrieving children when their estranged spouses or partners take children and leave the country. Some countries, like Japan and India are particularly difficult to deal with in getting these children back. Even when a U.S. court has awarded custody to the parent who remains back in America, the courts or authorities in these two nations seem to be unwilling to offer assistance in finding or retrieving children. I can tell you from a long-ago experience with a client whose young child was taken by an upset ex-husband and lodged with his mother, that it is a very upsetting thing for the parent and child alike and very difficult to solve, legally.
It is a distressingly common problem for an ex-spouse or estranged spouse or partner to take a child during or after divorce proceedings, when that person does not have legal custody. Often, the kidnapper is "correcting" their perception that the judge made a mistake in awarding custody to the other parent. Or, perhaps, that person is punishing the other parent in some way by taking the child. Or sometimes, they feel they are rescuing the child. In all cases, it is a terribly upsetting thing to have the child stolen away.
The National Conference of Commissioners on Uniform State Laws has promulgated two related uniform laws on the matter:
Uniform Child Abduction Prevention Act
Uniform Child Custody Jurisdiction and Enforcement Act
Regarding the international aspects, the United States is signatory to the Hague Convention on the Civil Aspects of Child Abduction (signed Oct. 25, 1980). Here is a list of the signing states. Japan and India are our two largest allies who are not signatory, though other Asian nations are problematic as well. The State Department is the major federal agency that works with parents trying to locate and regain custody of their children who have been taken overseas by noncustodial parents. The Globe article states that they have increased staff assigned to this issue from 18 to 65 in the past 3 years, and one of their jobs is to persuade non-signatory nations to sign the Hague Convention. Apparently, Representative Chris Smith of New Jersey is considering sponsoring a bill in the House to create a federal Office on International Child Abductions. This is mentioned in the Globe article and in several related articles gleaned from Associated Press and other news sources. On the Congressman's webpages, though there is nothing listed in the compilation of laws authored by Chris Smith. And his news page does not list anything to do with such a bill yet, so perhaps it is only in the planning stages.
The International Child Abduction Remedies Act, 42 USC §11601 et seq. (click on "next" to see the next part of the law), details the procedure in federal and state courts. The Department of State is the agency to contact in this matter. The Travel Bureau has an Office of Children's Issues, which includes abductions.
You may also want to know about the Polly Klaas Foundation, which was named for a 12 year old girl abducted from a slumber party in a family home in Petaluma, California. An international, high-tech search for Polly ensued, fruitlessly, which ended nine weeks later, when Polly's remains were identified, and thousands of people mourned this child which many had never met. But during the time of the search, many parents with lost children had come together through this search, sparking something new, which grew into a grassroots movement. They will send you a child safety kit to prevent abductions, as well as assist parents in tracing lost children and retrieving them. It looks like a very worthwhile site, and takes donations if you are so moved.