Al Jazeera has spoken to the parents of Kenyan youth recruited by the Islamist group al-Shabab to fight in Somalia.

Nobody is sure how many Kenyans al-Shabab have recruited, many coming from slums in the capital Nairobi.

But people who have been watching the process believe it runs into the hundreds, with only a handful of them are from ethnic Somali communities.

The vast majority of the recruits are from other tribes across Kenya, and that makes it much harder for the authorities to spot.

Kenya's military has been battling the fighters inside Somalia, and now the families of the youths recruited by al-Shabab say they fear retaliation.

Al Jazeera's Peter Greste reports from Nairobi.