(BBC) – It was a normal school day in May when Stephen and the 80 or so pupils were packed into classroom number 8 in South Sudan. But as the children listened to the words of their teacher, soldiers from the rebel forces surrounded the school’s pale-blue, concrete classrooms. Stephen describes being frozen with fear as the rebel fighters took him and more than 100 of his classmates. They were given no choice. They were now the latest young recruits, in South Sudan’s bloody civil war.