The IKO Center assists everyone who is confronted with (impending) international child abduction. They give legal advice, guidance, mediation and information. Unlike the Central Authority, the IKO Center is an independent foundation. It receives funding from the Dutch Ministry of Justice and Securtiy.
The Central Authority for International Child Affairs (CA) implements a number of conventions. Those conventions concern child abduction, adoption and child protection. It is a part of the Dutch Ministry of Justice and Security. Their tasks are described in The Hague Convention.
In conclusion, the IKO Center is the first to call for help and information. But if you wish to file an official return request, you need to contact the Central Authority.