Child-soldiering appears as a phenomenon dense with complexity, how its persistency testifies. The main challenge for international law concerns the twofold legal status of child-soldiers: not only victims of international crimes, but even criminal perpetrators themselves. Against such scenario, international law has pursued the child’s best interests principle within a twofold dimension, following the rationale upon which article 3 of the Convention on the Rights of the Child of 1989 is based. On one side, the protection of child-soldiers as victims has been achieved on the ground of substantive law; on the other side, the criminal accountability of child-soldiers has led to a paradigm shift, by which the principle of the best interests has been evaluated under the procedural dimension.