Imagine if 5 million refugees arrived suddenly in Australia. That is roughly the equation facing Lebanon.

The influx of Syrians escaping civil war has increased Lebanon's population from 4 million to 5 million in the space of a few years.

This year has brought the most dramatic and sudden rise in refugee numbers: a surge of over 500 per cent.

Almost one in five residents in Lebanon is now a refugee.

In a nation already balanced along delicate sectarian lines, the jump in Syrian refugees represents a serious strain.

The Lebanese government is wary of the new arrivals.

It allowed Palestinian refugees to move in and stay after the creation of the state of Israel in 1948.

A young Syrian refugee in the Marj refugee camp. ( ABC News: Hayden Cooper )

Their presence played a lethal role in Lebanon's own brutal civil war, which lasted 15 years and destroyed Beirut as Israel laid siege to Yasser Arafat and the militants of the Palestine Liberation Organisation (PLO).

But today, Lebanon does not want the new round of refugees to stay, so it is refusing to allow Syrians to build permanent structures to live in.

Instead, they try to blend into the local population, or they live in tents dotted around the Lebanese countryside.

At one such camp, near Marj, in Lebanon's Bekaa Valley, 300 refugees are struggling through a bitter winter.

Everywhere there are children: 78 per cent of the 2.3 million refugees surrounding Syria are women and children.

At this camp, the statistic is obvious. And what's worse – very few, if any of the children in this camp are enrolled in school.

Young refugees desperate to learn

Boushara Darwish, 14, recites the alphabet and counts to 10 in English. But she has not been to school in two years.

"I hope one day I can become a teacher," she said from the dark confined space of her UNHCR tent.

Syrian refugee Amani Darwish (left) and her father Ahmed Darwish. ( ABC News: Hayden Cooper )

"I used to love learning. I really hope that I can go to school here because I already lost two years and I don’t want to lose more."

Her sister, Amani, is 12. She should be in grade six, but she too has lost two years of schooling.

"I want to go to school and study. That's what I like," she said.

Their father, Ahmed Darwish, fled Syria with his family six months ago.

The 37-year-old cannot work because of an injury sustained in a shelling near his home in Damascus.

He says life in the refugee camp is taking its toll.

"The situation is very bad here. The tents leak. There's no heating, and we're cold all the time," she said.

"The children are always coughing.

"They always have a cold and flu. I can't afford to buy them medicine because I don't have money."

'We don't have any money'

On the day the ABC visited the camp there was a delivery of aid for the refugees.

Local politicians were handing out supplies, but they seem more interested in the photo opportunity than actually helping.

Ahmed tried to get a heater, but he was ignored. Ahmed's brother, Nour Darwish, is just 16.

His face and hands are disfigured from burns sustained in a shelling attack on his home in Damascus.

"I can't find a job. I need cream for my injuries because it's burning all the time, but we don't have any money," he said.

In Lebanon alone, hundreds of thousands of children do not attend school.

They are the lost generation of Syria's war.