Jandark Benham Mansour Nassi, 55, and her son Ismail, 16, spoke to the Catholic charity Aid to the Church in Need about their horrific experiences which began when they were taken from their home in the village of Bartella near Mosul in August 2014.
Ismail claims that he was initially jailed by the group and said whilst incarcerated he witnessed a woman being stoned to death and a man being shot in front of him.
The teenager told the charity he was forced to pretend to convert to Islam in order to save his life.
Ismail said: "The terrorists told me: 'If you do not convert to Islam, we will shoot you as well'. That is when I converted to Islam. From that time on, we concealed that we were Christians."
"Daesh made me go to a correctional camp. I had to grow out my hair and grow my beard," Ismail revealed, "My mother got a black, concealing robe, but was not allowed to go on the streets. Daesh warriors wanted me to marry, so I would be one of them. I objected, stating that I was too young: 15 years.
"They were not impressed, because even boys of 13 were married. The terrorists wanted me to join them. They were convinced: 'Our state will survive everything.'"
When Qaraqosh was liberated by Iraqi troops in October 2016, the pair said that IS troops fled Mosul but took civilians with them to use as human shields.
The pair only escaped when the Jihadi fighters became preoccupied with fighting.
They managed to find refuge in a house and "After hours of fighting, my mother and I were able to leave the house, waving a white flag. Soldiers of the Iraqi liberation army welcomed us. We were free," Ismail claimed.
The Iraqi offensive in Mosul is now entering its twelfth week.