23 June 2014 Last updated at 14:32 BST
Two men from the city have been identified taking part in what appears to be a Jihadist recruiting video, which was posted online last week.
It is thought Reyaad Khan travelled to Syria with friend Nasser Muthana who also appears in the footage.
An expert on radicalisation, Dr Suraj Lakhani of Cardiff University, said: "As far as I'm aware, there has been an issue in Cardiff for a while now."
Nicky Smith spoke to one of the families and the local community, while Jordan Davies speaks to Sheikh Zane Abdo, Imam at the South Wales Islamic Centre.

Hawkins, 24, finished ninth in the Rio Olympic final in August in only his third attempt at the distance.
"We are delighted to confirm Callum's selection," British Athletics performance director Neil Black said.
"We can already see his talent, finishing eighth at the London Marathon then a brilliant ninth place in Rio."
In October, Hawkins became the first Scot to win the Great Scottish Run since 1983, setting a Scottish half-marathon record in the process with his time of 60 minutes 22 seconds.

The government and private operators run TV and radio stations and outlets from American Samoa are readily available.
By June 2015, there were nearly 27,000 internet users (InternetLiveStats.com). Internet cafes are widely used.

It is the work of street artist Joe Caslin, who rose to public attention during last year's same-sex marriage referendum in the Republic of Ireland.
The Belfast artwork is similar in style to another huge mural of his in Dublin, which depicts two young men embracing.
The artist said he felt the time was right to take the campaign to Belfast.
"Northern Ireland is the only territory now on the islands of western Europe that doesn't have same sex marriage - and it's same-sex marriage not civil partnership," he told BBC Radio Ulster.
"Through the work that I did in Dublin last year with the referendum and the large piece we put up on George's Street, I felt it was an ideal time, coming up to the Pride Festival that takes place this weekend, to reignite that conversation."
The street artist, from County Roscommon, also works as an art teacher at a secondary school in County Offaly.
He said he received a positive reaction from many members of the public in Belfast who stopped to watch him work on the mural in Hill Street.
The new mural, entitled Love Wins, features an embrace between two women who live in Belfast.
"They travelled to America to get married last year," the artist said.
The pair could not have held the ceremony in their home town.
Same-sex marriage became legal in England and Wales in March 2014 and in Scotland, the first gay weddings took place on 31 December 2014.
In May 2015, the Republic of Ireland became the first country in the world to legalise same-sex marriage through a popular vote, with the law taking effect in November last year.
Earlier this month, a couple from the Isle of Man became the first to change their civil partnership into a marriage on the island.
The Northern Ireland Assembly has held a number of votes on the issue and last year, for the first time, a majority voted in favour by the narrowest of margins.
MLAs supported the motion by 53 votes to 52, but it was blocked after the Democratic Unionist Party (DUP) deployed a petition of concern that required the proposal to achieve a cross-community majority.
Those who oppose same-sex marriage have argued that marriage should be between a man and a woman.
They have claimed legalising same-sex marriages undermine family law and a child's right to father and a mother.
Cardiff has an ongoing problem with the radicalisation of young Muslims, said an academic who has studied the issue.
[NEXT_CONCEPT]
Scottish marathon runner Callum Hawkins has become the first athlete selected for the British team at the London 2017 IAAF World Championships.
[NEXT_CONCEPT]
Press freedom is "generally respected", according to US-based Freedom House.
[NEXT_CONCEPT]
A five-storey mural depicting a married lesbian couple has been painted on a city centre building in Belfast, as part of the same-sex marriage campaign.