At least 20,000 children remain inside besieged Fallujah in Iraq, a stronghold of the self-styled Islamic State near Baghdad, the United Nations' children's agency has said.
The children face the risk of forced recruitment in the fighting and separation from their families, UNICEF added.
"We are concerned over the protection of children in the face of extreme violence," UNICEF Representative in Iraq Peter Hawkins said in a statement.
"Children face the risk of forced recruitment into the fighting" inside the besieged city, and "separation from their families" if they manage to leave, he added.
Backed by Shia militia and air strikes from the US-led coalition, the Iraqi armed forces launched on 23 May an offensive to recapture Fallujah, 50km west of Baghdad.
The assault on Fallujah is expected to be one of the biggest battles ever fought against so-called Islamic State.
Fallujah was the first Iraqi city that fell under control of the ultra-hardline Sunni militants, in January 2014.
About 50,000 civilians remain in the city, according to the UN.
Iraqi security forces operating in the city systematically separate men and boys aged over 12 from the families to investigate possible links with the self-styled Islamic State.
"UNICEF calls on all parties to protect children inside Fallujah, provide safe passage to those wishing to leave the city and grant safe and secure environment to civilians who fled Fallujah," Mr Hawkins said.
Iraqi forces continue advance
Footage from the city shows Iraqi soldiers firing at targets in their battle with IS militants.
The Iraqi army's assault is backed by world powers including the United States and Iran.
A week after Iraq announced the start of the assault, its troops advanced in large numbers into the city limits for the first time on Monday, pouring into rural territory on its southern outskirts but stopping short of the main built-up area.
Iraq describes the assault to retake the city as a potential turning point in its US-backed campaign to defeat the ultra-hardline Sunni Muslim militants who rule a self-proclaimed caliphate across much of Iraq and Syria.
