7 October 2014 Last updated at 23:27 GMT

By Linda Pressly BBC World Service, Kosovo

In Kosovo it used to be the case that families were culturally Muslim, but rarely devout believers. Recently though some young people have become radicalised. Up to 200 are thought to be fighting in Syria and Iraq causing heartbreak for those left behind.

"In these pictures of him as a little boy, his eyes are so innocent."

Arieta is leafing through a pile of photos of her younger brother, Blerim Heta. She does this every day, and cries a little.

"My brother had a wonderful life. He had money. He didn't have a Mercedes, he had an Opel, but we were a happy family. And I can't understand why he did that."

Blerim was 24 when he left Kosovo on 7 August 2013, without a word to his family. Two days later Arieta got a text - he said he was in Turkey. She didn't worry, because after becoming a devout Muslim, he often travelled to hear different imams preach. Then she called his number and a message flashed up on her screen - "Welcome to Syria."

When Arieta talked to Blerim on Skype, he denied he was in Syria - he insisted he was in Turkey, learning Arabic and looking for a wife who wore the hijab. Arieta wanted to believe him, but then her mother found a postcard Blerim had written and left in his bedroom.

"It was a goodbye postcard. He had written that he was on a journey and that he wouldn't come back," Arieta says.

Like many Kosovans, her family identifies culturally as Muslim, but was never religious. Then Blerim started going regularly to the mosque. He began travelling to Macedonia across the border, and to mosques in other Kosovan towns.

"There is one boy in particular - I still see him around every day. He was the one who influenced my brother. He didn't buy Blerim a ticket to Syria, but he took him to the places where they said jihad was a good idea. I hope that one day, that boy is judged for what he did," Arieta says bitterly.

In his last three months in Kosovo, Blerim Heta changed. He grew a beard. He wore his trousers shorter, like some Muslim men in the Middle East. And he watched a lot of YouTube videos of imams preaching. Then he was gone.

Eventually, on Skype, Blerim Heta confessed to Arieta that he was, indeed, in Syria.

"He told me he's fighting for his religion and that other people are bad. He said he wanted to die for Allah, and that it would be a great pleasure for him. I started to cry and scream and say to him what kind of religion do you have to kill people, to kill yourself? And he said if you speak to me like that, I will never call you again."

Arieta did not tell the family that Blerim was in Syria - she did not want to alarm them, and part of her still believed he would come home.

Erion Abazi's family hope he will come home to Kosovo too. Erion is eight years old.

On Thursday, 10 July Erion's mother, Pranvera, got a text from her husband, Arben. "It said he was in Syria with Erion and that he would call her back later," recalls Pranvera's cousin, Suad Sadullahi.

Arben left home on Monday 7 July, telling his wife he was taking their son on an excursion to the mountains in Kosovo. Instead he took Erion across the border to Albania, and then flew from Tirana to Turkey, before travelling on to Syria.

The family is still in shock, and has only had sporadic contact with Erion. On 15 July, there was a text from Syria to say Erion was OK. Suad called the number. An Albanian-speaking man answered aggressively, and Suad persuaded him to let them speak to Erion.

"I was asking Erion, where are you, where is your father… and he said, my father is in a training camp, and I am very far away. I passed the phone to Erion's mother, Pranvera, and she talked to him for a while before she was cut off."

The pictures of Erion on social media show him holding up one finger in the Islamic State (IS) sign, and tumbling around with other children next to the militants' black flag. Suad thinks Erion is living with Albanian-speaking families from Kosovo, Albania and Macedonia somewhere in Syria.

The authorities think 200 Kosovans may be fighting with militant groups in Syria and Iraq. "We know there are quite a large number of Albanian families over there with the wife and children too," Saud says.

He believes often Kosovans with extended family in Syria, remain silent. There is a stigma now in Kosovo at being associated with radical Islam. And there is also fear: Perhaps you could lose your job if it is known your son has gone to join IS militants?

About 70 people have been detained by police in connection with investigations into Islamic extremism as Kosovan authorities become increasingly alarmed.

On 15 September Pranvera and Suad saw Erion on Skype. "It was the biggest relief for us to be able to see him and to hear his voice," says Suad.

But Erion had changed. "We thought he was more grown-up - maybe because he's had his head shaved. To me, he was speaking more like a man - and he's only eight years old."

Erion's family were all aware his father was becoming more religious. But it was only after her son's disappearance that Pranvera told them her husband asked her to wear a hijab, and talked about going to Syria.

"But not in million years did she ever think he would take Erion," says Suad.

Before he left for Syria, Arieta says she thinks her family ignored the signs her brother, Blerim Heta, was being radicalised - his change of dress, his beard.

"At that time we believed he wasn't a stupid boy. He was a good boy, but I think he was brain-washed. First they scared him with things that would happen to him in hell. Then they told him the positive side, about paradise. I know this because I found some notes he had written."

On 24 March this year, Blerim called his family in Kosovo.

"I asked him - are you coming home? Mama wants to see you and she's very sad," remembers Arieta. "He said to me, 'You don't know what you are doing, you people. Only Islam is the right thing.' And he said, 'Maybe today or tomorrow I will meet Allah.' Then he talked to my mother and he said, 'Just forgive me… Forgive me all I've done?"

On 25 March Arieta's brother killed himself and 52 Iraqis in a suicide bombing.

Arieta struggles to comprehend how and why her brother changed.

"When he was in Kosovo, Blerim said that suicide bombers, they're not Muslims. But when I talked to him in Syria, and I asked him, 'Is it good to kill people?' He said, 'If they're not Muslim, yes.'"