A child plays with the debris of his house.

When an Israeli air strike targeted a security office near her home in Gaza this month, 10-year-old Zeina Dabous frantically scribbled a note and slipped it under her mother's pillow.

Though a ceasefire has since Friday halted the air raids, experts warn that children in the besieged coastal strip will likely carry the mental scars for years to come.

Psychologists say many are showing signs of depression, anxiety, behavioural disorders or irritability, and many are wetting their bed.

At home in Gaza city just before the bombing stopped, Zeina said she was constantly petrified and barely sleeping.

After a strike hit very close, "before sleeping I wrote a note in red pen to my mother and slipped it under the pillow because I was scared I would die," she said.

Zeina is one of around a million children living in Gaza, according to the UN's children agency UNICEF.

 Palestinian children play with toy guns next to the rubble of a house.

'Don't be scared'

When the last war raged, Zeina was no older than four.

The charity Save the Children on Friday warned that children in Gaza would suffer for years to come.

They "are suffering from fear and anxiety, a lack of sleep, and are displaying worrying signs of distress, such as constant shaking and bedwetting," it said.

In their grandfather's home, Maysa Abu al-Awf, 22, held her two-year-old brother Ahmad on her lap and tried to comfort him after they lost two sisters and dozens of relatives in a devastating air strike.

After air strikes demolished their four-storey family home in Gaza city on Sunday last week, Maysa, little Ahmad and their sister Maram, who is seven, screamed for hours under the rubble before they were rescued.

 'Catastrophic number'

In the Gaza Strip's main Shifa hospital, their 16-year-old cousin Omar was in shock after the same strike killed his two brothers and father, who was the head of internal medicine at the facility.

He had stopped talking, his family said.

There is no overall tally of how many children are suffering from mental health issues in Gaza due to repeated conflict, the GCMHP says.

But it said it records hundreds of new cases a month.

Psychologist Mohammed Abu Sabeh said children exposed to "great trauma" often then exhibit "violent behavioural disorders".