Further information is available here; the deadline for applications is January 4, 2012.  This is the posted job description:
He or she will work in the areas of international family law and international child protection and be part of a team, under the direction of the responsible First Secretary, supporting the 1980 Hague Child Abduction Convention and the 1996 Hague Child Protection Convention. Additionally, the Legal Officer will work on a variety of projects arising from recommendations made by various Special Commissions, including international family mediation and the private international law issues surrounding the status of children (including international surrogacy arrangements).

Duties may further include comparative research on general aspects of cross-border family law, work on the international child abduction database (INCADAT), drafting of research papers and other documentation, drafting and general preparation of materials for publication, answering daily requests for information relating to the relevant Conventions, preparation for meetings (including Special Commission meetings), assistance in the preparation of and participation in conferences, seminars and training programmes, giving presentations and lectures on issues related to international family law, and such other work as may be required by the Secretary General from time to time.