But what if one day they do leave, closing the door behind them for the last time?

Soon after, Victoria Police or the AFP knock on the door, and tell you that your child has left Australia to join a foreign conflict.

It is not always that straightforward, of course, and Melbourne researchers are set to discover just how varied the paths to extremism can be.

A Victoria University and Victorian Arabic Social Services project starting next month will involve interviewing those who have had family members join extremist groups such as Islamic State. It aims to build an understanding of how to support families, and prevent those at risk of radicalisation from leaving in the first place.

Researchers aim to interview people from 10 families who have had a member travel overseas, and from 10 families at risk of having a member travel overseas.

Michele Grossman, director of the Centre for Cultural Diversity and Wellbeing at Victoria University, said: "Young people who are leaving, the families have just no idea. Then, all of a sudden, wham, you find out what they've done.

"Then [family members] starting eating themselves up, thinking, 'Where did I go wrong? What did I miss?'"

The project, which received a $100,000 state government grant earlier this year, will not necessarily be looking for common ground, but for a broader understanding about how a young person can lose their way.

"It is foolhardy to try to over-profile violent extremism," Professor Grossman said. "Every pathway is unique, and we stand to learn more from the anomalies than the consistencies.

"We're trying to build as rich a picture as possible."

Matt Di Lorenzo, a Victorian Arabic Social Services project officer, said that in the past three years the organisation had increasingly been contacted by people seeking advice about their family members travelling overseas to join foreign conflicts.

The research may reveal information that is also new to authorities, because some family members may not be as open with police or intelligence agencies while the fate of their loved ones is unknown.

"There's definitely a lot of fear of involvement with law enforcement at the early stages, because obviously they don't want their daughter or son to go to prison," Mr Di Lorenzo said. "And they really don't know what could happen to them."

The number of foreign fighters leaving Australia has dried up in the past year, but the federal government estimates that about 110 Australians are fighting in Syria and Iraq.

It has cancelled 145 passports of suspected jihadists attempting to travel to conflict zones, suspended 26 passports and refused applications for a further 22 in the past financial year.

Most of those known to have left Victoria for Syria or Iraq are men aged in their late teens or early 20s and from a variety of ethnic backgrounds, including people of European, African or Middle Eastern descent.

Professor Grossman said the findings from the research would be used to frame deradicalisation strategies.

But she did not want to create the violent extremism equivalent of the "worried well", a term used to describe people who do not need medical assistance, but visit the doctor anyway for reassurance.

"Shared experiences across families are very important, but so too are outlier experiences than can also provide us with vital insights," she said. "Families feel very alone with these problems."