At least 24 children in Germany, many of whom are as young as 13, have reportedly joined and fought the war in Syria and Iraq for the Islamic State.

Out of this 24 children who fled from Germany to fight for the ISIS, five have returned to the country with combat experience, noted a report, which sourced to the German Intelligence Agency.

"The youngest was 13 years old," Hans-Georg Maassen, head of the Federal Office for the Protection of the Constitution (BfV), told Rheinische Post.

There were four minor girls as well, among the children who went to Syria "with the romantic notion of jihad marriage", he pointed out.

Underage girls have reportedly been married to young jihadi fighters, whom they met on the internet, Maassen revealed.

"These young people are blinded and do not even know what to expect."

In most cases, the intelligence agencies were approached by parents after they found that their children are "missing".

The state security agencies have found that overall around 400 Germans have joined the jihadists in Iraq and Syria.

A recent report in The Local noted that most of the ISIS recruits from Germany were young men coming from poor educational background, with many being school dropouts and the others unemployed.

The report found that among the 378 German Islamists who joined the ISIS since mid-2012, just one in four finished high school.

It further found that only 6% of ISIS supporters from Germany finished post-school training and only 2% had some higher education. The report also stated that only one in five ISIS radicals in Germany was registered as unemployed and just 12% had a job. And those who worked were mainly employed in low-paying jobs.