Backed by aerial support from the US-led coalition and paramilitary forces mainly made up of Shiite militias, Iraqi government troops more than a week ago launched a military operation to recapture Fallujah which has been under control of the extremist group for more than two years.
As the battled unfolded -- with Iraqi forces this week pushing into the city's southern sections after securing surrounding towns and villages -- more than 50,000 people are believed to be trapped inside the Sunni majority city, about 65 kilometres west of Baghdad.
"Children who are forcibly recruited into the fighting see their lives and futures jeopardized as they are forced to carry and use arms, fighting an adults' war," the organization said in a statement.
It called on "all parties to protect children inside Fallujah" and "provide safe passage to those wishing to leave the city."
Fallujah was the first large city in Iraq to fall to IS and it is the last major urban area controlled by the extremist group in western Iraq. The Sunni-led militants still control the country's second-largest city, Mosul, in the north, as well as smaller towns and patches of territory in the country's west and north.