A/HRC/40/49 challenges. She also met with the Director-General of the European Civil Protection and Humanitarian Aid Operations to discuss common areas of interest. The work of the European Union and its member States on human rights and peace and security issues, as well as the presence of the European Union in all countries on the children and armed conflict agenda, are important multipliers for the work of the Special Representative. The European Union guidelines on children and armed conflict, the implementation strategy for the guidelines and the checklist for integration of the protection of children affected by armed conflict into the Common Security and Defence Policy missions and operations are crucial tools to integrate child protection in all European Union actions. In November 2018, the Special Representative opened the United Nations Liaison Office for Children and Armed Conflict – Europe in Brussels, which, inter alia, will enhance cooperation with the European Union institutions and member States. The Liaison Office also covers the Special Representative’s relations with NATO, the Human Rights Council and other Geneva-based mechanisms, as well as Europe-based non-governmental organizations (NGOs). North Atlantic Treaty Organization 52. The Special Representative has continued working with NATO to strengthen its child protection architecture. In October 2018 in Brunssum, Netherlands, her Office supported training on children and armed conflict for NATO child protection focal points. Her Office also worked with the NATO child protection adviser to take stock of the lessons learned and best practices of the NATO policy on children and armed conflict in Operation Resolute Support and contributed to the update of a policy document entitled “The protection of children in armed conflict - the way forward”. From 23 to 24 October 2018, her Office participated in the United Nations-NATO staff talks, at which it was agreed that the United Nations and NATO would move forward on strengthening cooperation on children and armed conflict with a particular focus on capacity-building and awarenessraising. D. Working with human rights entities and United Nations mechanisms 53. With a view to achieving universal ratification of the Optional Protocol to the Convention on the Rights of the Child on the involvement of children in armed conflict, the Special Representative has continued to engage with Member States that have not yet ratified the instrument. She held bilateral meetings with Member States and actively engaged with regional and subregional organizations, civil society and regional groups on the matter. Following continued advocacy by the United Nations in South Sudan and the visit of the Special Representative in September 2018, the country deposited the accession instrument to the Optional Protocol on the involvement of children in armed conflict at United Nations Headquarters in the margins of the high-level debate at the seventy-third session of the General Assembly. South Sudan became the 168th State party to the Optional Protocol. The Special Representative also used her engagement with Member States to push for the endorsement of other instruments that will improve the protection of the rights of children in situations of armed conflict, such as the Principles and Guidelines on Children Associated with Armed Forces or Armed Groups, the Safe Schools Declaration and the Vancouver Principles on Peacekeeping and the Prevention of the Recruitment and Use of Child Soldiers. 54. The Special Representative continued to cooperate closely with international charter- and treaty-based human rights mechanisms, in particular the Human Rights Council, the Committee on the Rights of the Child and the Human Rights Committee. Regarding the Human Rights Council, her Office submitted one contribution in the previous reporting period to the universal periodic review of Colombia. During the ensuing interactive dialogue in May 2018, many Member States highlighted the protection needs of children in the context of the armed conflict in Colombia, thus reiterating the points noted in the Special Representative’s submission. Member States recommended that legal measures to prevent child recruitment by armed groups be strengthened and stressed the need to ensure that demobilized children are reintegrated and rehabilitated. Colombia has endorsed those recommendations and the Office of the Special Representative has been 14