This policy and practice note describes the methodology of the non-governmental organization (NGO) Geneva Call to engage armed non-state actors (ANSAs) in protecting children from the effects of armed conflict. ANSAs cannot take part in the development of, or become party to, international treaties, so Geneva Call has developed an innovative mechanism, the ‘Deed of Commitment’, by which ANSAs subscribe to specific norms. The approach starts from the premise that ANSAs should not just be considered part of the humanitarian problem, but also part of the solution. Efforts to engage ANSAs on protection of children built on Geneva Call's earlier experience and the trust built up with ANSAs in developing and implementing a Deed of Commitment banning the use of anti-personnel (AP) mines. The Deed of Commitment on children and armed conflict, however, is more complex, having to take account of the agency of children, a more convoluted legal framework, and the existing United Nations (UN) Monitoring and Reporting Mechanism on children and armed conflict (MRM). In drafting the Deed of Commitment, Geneva Call consulted ANSAs and convened an expert group of legal and policy experts on children and armed conflict. These consultations made clear that the use and recruitment problem is not black and white, as, for example, in many cases ANSAs are intertwined with supportive communities, and often ANSAs take on protective roles – or at least perceive themselves to do so – due to lack of security and absence of assistance. Consequently, the problem needs to be addressed within a comprehensive approach to child protection and ensuring children's rights. The Deed of Commitment on children and armed conflict – similar to its predecessor banning AP mines – includes provisions on implementation and verification by both external monitoring and self-monitoring. Challenges to monitoring and verification include those posed by states which deny or obstruct access to ANSAs or territories where they operate. Complex problems such as protecting children from the effects of armed conflict require a range of responses. While the MRM – a political and process-driven mechanism based on an essentially punitive approach – will continue to be a key mechanism, it is important to have complementary approaches to engage ANSAs in committing to and complying with norms for child protection in armed conflict. The text of the Deed of Commitment is included as an appendix.