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.
Cardiff has an ongoing problem with the radicalisation of young Muslims, said an academic who has studied the issue.