The militant group’s black flag also featured in materials given to children at the ISIS-run school that Abu Shahed’s son was forced to attend after the militants captured the Syrian town of Al Bukamal in 2014.

“My son changed a lot at school and became very pro-ISIS,” said Abu Shahed, who now lives in Turkey with his family and like others interviewed by NBC News did not want to give his full name out of concern for relatives sill living in Syria.

“Me and my wife knew that we had a little spy at home,” he said.