Insurgent groups are registering births in territories which they control, and yet States do not recognize insurgent birth registration, resulting in a legal vacuum with harsh consequences for children. Based on international human rights and humanitarian law provisions related to birth registration, this article argues that insurgent groups have an inherent power to register births in order to fulfil their obligations under international humanitarian law, and that State obligation to ensure the right to recognition as a person under the law should require States to recognize insurgent birth registration in order to prevent harm to children.