( CNN ) Zarine and Shafi Khan saw their son growing distant for months . But they say they did n't realize what was happening -- until it was too late . `` For the past few months , he was very quiet and he wanted isolation because he was watching or doing something on social media . And that 's why he was brainwashed , '' Zarine Khan said in an exclusive interview with CNN 's `` AC360 '' Thursday . Now Mohammed Hamzah Khan , 19 , is accused of trying to support ISIS . This week he pleaded not guilty to a federal charge of attempting to provide material support to a foreign terrorist organization . Outside the courtroom in Chicago , his mother told reporters she had a message for the terror group 's leader : `` Leave our children alone . '' `` They 're misusing the children 's innocence , '' Zarine Khan told CNN 's Anderson Cooper Thursday . `` The children are gullible . They 're vulnerable . Their thinking skills have not completely developed and these people are preying on that . '' ISIS , an extremist Islamist group , has been fighting to take over a swath of territory in Iraq and Syria , where it wants to establish a caliphate or Islamic state . The group regularly uses social media to promote its goals , posting videos of brutal violence and using hashtags for other stories in the news to disseminate its message . Authorities arrested Mohammed Khan at O'Hare International Airport in October as he was about to embark on a flight to Istanbul . In a letter he left behind for his parents , he wrote that he was leaving the United States and on his way to join ISIS , according to a criminal complaint . He invited them to join him in the `` Islamic State , '' but he warned them not to tell anyone about his travel plans . The letter shocked them , his mother said . `` The things in those letters did not reflect the upbringing they got . Those values , they do n't come from us . It was so out of sync . It was so out of place , '' she said . Thomas Durkin , the teen 's attorney , said the case was a sign of `` nothing but immaturity . '' `` There are thousands of kids doing this , and I think that 's part of the point , what 's causing them to do it ? I do n't believe , in my client 's case , it 's because he 's a violent person and wants to go kill people , '' Durkin said . `` I think he was a misguided young man who got manipulated by social media . '' During questioning at the airport , Mohammed Khan told FBI agents that a person he met online had given him the phone number of a person to call once he arrived in Istanbul , federal authorities said in October . That person , Khan allegedly told the agents , was to take him to ISIS territory . According to the complaint , Khan told authorities he was planning on being in some type of public service -- like a police force -- or providing humanitarian work or in a combat role . ISIS has successfully recruited large numbers of foreign fighters from across the globe , including from the United States and Western Europe . Turkey , the complaint notes , is a common transit point for foreign fighters from Western countries who travel to join ISIS . If it were n't for the Internet , his mother now says , `` he would never be in the situation he is in today . '' So what 's her message for other parents ? `` Maybe the mistake we made was maybe we protected our children . We were trying to protect our culture or values . Maybe that was a mistake , '' Zarine Khan said . `` I would tell them to expose their children more to what 's going on in the world , help them develop critical thinking skills to differentiate between the good and the bad guys . '' CNN 's Michael Martinez and George Howell contributed to this report .
Mohammed Hamzah , is accused of trying to support him . The Illinois teen 's father on social media brainwashed his son .