At just 15 years old Farhad Khalil Mohammad Jabar from Parramatta is part of a growing trend worldwide – that of teenagers being radicalised at younger and younger ages.

His act of terrorism in Sydney came on the same day another 15-year-old boy in the UK was sentenced to life in jail for plotting an Anzac Day massacre in Melbourne.

It also follows a forum held by concerned community members and leaders on how to combat violent extremism among youth held in Bexley last week and warnings from the head of the Australian Security Intelligence Organisation (ASIO) Duncan Lewis that teenagers are being radicalised much more quickly and at younger ages than ever before.

Online radicalisation expert at Edith Cowan University Robyn Torok​ said in June that Islamic State had released a new book aimed at 13- to 20-year-olds living in the West, explaining how to get away with terrorist attacks.

"It actually talks about how to be a young person and to blend in ... to be a lone wolf terrorist in the West," she said. "It's engaging, and a 13-year-old can understand it and act on it."

While the book had been mocked by some commentators, Dr Torok said it should be taken seriously as it encouraged the teens to hide what they were doing from their family and friends while at the same time normalising the behaviours in their minds.

She said social media activity from a number of different groups had also become more intense since Australia expanded its bombing from Iraq to Syria.

When the British teenager planed his attack at just 14, he was an active member of a growing global network of radicalised youths organising themselves on Twitter, said Dr Amarnath Amarasingam​, from the University of Waterloo in Canada.

"They call themselves a family," Dr Amarasingam told Fairfax Media. "It's a growing phenomenon, I don't think we've seen it to this extent in the past. There has been a mass mobilisation of not only fighters from around the world but all these youths who are supporting [IS]."

Dr Amarasingam is researching the radicalisation of Muslim youths, contacting them in order to discover what motivates them to act as a propaganda "megaphone" for jihadists in Syria or elsewhere.

"Centred on Twitter and Facebook, they call themselves the Baqiya family," Dr Amarasingam said. "They consider themselves to be this close-knit community online ... Twitter is the epicentre. You can be in direct communication with a fighter in Syria within about 15 seconds. That's part of the appeal, a lot of these youths feel like they're part of something, for the first time they're part of something greater than themselves."

It is hard to gauge how large the Baqiya family is, but by one estimate it's 40,000 members, and growing. The vast majority are 20 to 28, but quite a few are 18 or younger, male and female.

But other changing trends apart from age are emerging, according to Anne Azza Aly from the Countering Online Violent Extremism Research Program at Curtin University.

Dr Aly told Fairfax Media she has begun compiling a database of 100 "self activators" around the world in an effort to compare and contrast trends and similarities.

Although her research is in its early stages, Dr Aly said what she has already noticed is that more and more young people being radicalised are attached to the violence first, rather than religion.

"Ten years ago older men were attached to ideology and immersed in the religious aspects first. Now more and more young people don't appear to have an intense ideology they have only a superficial attachment. They are driven by anger and violence."

Dr Aly is keen to find out why the problems of radicalisation are emerging and why a country like Australia has a bigger problem than a country like Singapore which has a lot of similarities and a bigger Muslim population.

"Part of it is the internet which is an echo chamber," said Dr Aly.

Muslim community leader Dr Jamal Rifi said parents talking to their children can help and he called on them to watch for early signs of radicalisation.

"I urge all parents, in particular fathers in the Australian Muslim communities to initiate a dialogue with their kids, teenage sons and daughters and to be alert for any changes in their behaviour and to seek help.

"The earlier the better.

"Please talk to your kids, please seek help early. Doing so does not mean you are getting them in trouble. It is the opposite. It means you are preventing them from getting in trouble and you might be saving their lives and the lives of others."