Children in the military are children (defined by the Convention on the Rights of the Child as persons under the age of 18) who are associated with military organizations, such as state armed forces and non-state armed groups. Throughout history and in many cultures, children have been involved in military campaigns. For example, thousands of children participated on all sides of the First World War and the Second World War. Children may be trained and used for combat, assigned to support roles such as porters or messengers, or used for tactical advantage as human shields or for political advantage in propaganda.