Abstract The principle of proportionality under international humanitarian law prohibits an attack if the expected harm to civilian persons and objects is excessive in relation to the anticipated concrete and direct military advantage. In this article we argue that, when applying the principle of proportionality, the incidental harm to a child must be given a higher value as compared to incidental harm to an adult. This reflects the broader framework of international humanitarian law, which creates stratifications amongst different groups of civilians and provides special protection for children in times of war. This aligns with the practice of many militaries, which tends to implicitly assign a heightened worth to the lives of children due to moral and political considerations. Such reasons stem from the perceived vulnerability of children as well as their moral innocence reflecting harmlessness and blamelessness. Indeed, harm to children’s lives tends to generate a greater backlash among the community to which they belong and, as a result, a military disadvantage. We argue that the greater weight assigned to the lives of children in proportionality assessments is not simply a matter of morality or strategic calculations, but in fact a requirement from a more wholistic interpretation of international humanitarian law.