This dissertation examines the conditions under which rebel groups commit to international humanitarian law with a particular focus on UN action plans to end and prevent child rights violations in armed conflict. Most researchers have simply considered an armed group's non-use of child soldiers to be a gesture of active commitment to international humanitarian law. However, such a presupposition overlooks the fact that some groups may not choose to use children or violate other types of child rights merely because they initially have no incentive to commit those violations and/or have viable alternatives. By focusing on the groups that have been blacklisted for violating child rights by the UN from 2002 to 2018, I examine conditions under which "naming and shaming" by international institutions changes rebel groups' commitment to international humanitarian law. The sequence of rebel groups' commitment to UN action plans is divided into four phases: violating child rights, listing violators, signing UN action plans, and complying with UN action plans. To examine this sequence, I use a mixed-method approach that consists of statistical analysis with large-N cases, qualitative comparative analysis (QCA) with medium-N cases, and congruence tests with small-N cases. First, I argue that rebel groups consider their legitimacy in the eyes of domestic and international audiences throughout the phases of violating child rights, as well as signing and complying with UN action plans. Second, I argue that a host state's motivation to blacklist its rebel group is the key factor in influencing the UN's decision to blacklist a particular rebel group. These findings contribute to the literature on international institutions and political violence by bridging theoretical approaches in both fields and considering new empirical evidence on rebel groups' behavior. By better explaining the determinants of rebel groups' commitment to international humanitarian law with a particular focus on rebel groups' efforts to gain a domestic and international reputation for legitimacy, my findings also have implications for current and future approaches to public policies for the protection of children in armed conflicts.