Gaza's boys and girls come out to play

London 2012 it isn't. But on Sunday a relay of 50 schoolchildren bearing an Olympic-style torch will start from Deir el Balah Elementary Boy's School in central Gaza on the 17km road journey along the Mediterranean coast to the UN compound in Gaza City. There, they will light a flame, less to commemorate the notorious white phosphorus bombardment which razed the main warehouse here during Israel's military offensive in January 2009, than to herald the start of something altogether more cheerful: the fourth annual summer games.

Throughout the summer a total of 250,000 children will be brought together every day – girls and boys in separate groups in deference to Gaza's traditionally conservative culture – for a fortnight by the UN Refugee agency UNRWA for something that John Ging, its Gaza Operations Director, points out is all-too rare in Gaza: "a moment of childhood and happiness".

The children of all ages will enjoy diverse supervised activities including drama, traditional dances like Dabka, swimming, sandcastle building, bouncy castles, volleyball, football, painting and origami. Having last year won a certified Guinness World Record for the most people flying kites at one time, the children will next month attempt another: the largest number – probably more than 6,000 – to bounce basketballs simultaneously.

A few days after a gang of around 25 masked and armed men scorched and vandalised one of 35 camps being prepared for the games, John Ging, Operations Director of UNRWA here, was visited by three 15-year-old girls from Rimal Preparatory School. All three were appalled at the attack which wrought some $20,000 worth of damage and included delivery of an ominously menacing message for Mr Ging himself. The girls' appeal was simple: please don't cancel the games because of what happened.

Mr Ging was touched – and quick to reassure them. Having devised the games four years ago, he told the girls he was not about to abandon them now. As one of the girls, Amani Sansour, later explained in articulate English: "When we met Mr John he told us he will never stop the project. We are very happy that the summer games will not be stopped. It's a big chance for children to have fun and happiness in their lives, and their human rights. They can practise their hobbies and do things like swimming. This is especially good for girls who can't go to swim together without their parents, according to the traditional culture here. Life is very hard here for boys and girls but harder for girls."

For Amani the extremists who carried out the May attack on the beach site south of Gaza City "don't work for our interests. They want us to stay at home". Her friend, Sawsan Kamel, agreed. "They are a minority," she said. "They don't represent our opinions." And for a third, Fatima Said – who having thought the games were only suitable for young children, changed her mind after hearing a talk about the range of activities – "what is important is that this year the games will not only be for refugees", the families of those who fled or were forced out of their homes in what is now Israel during the 1948 war and are UNRWA's direct responsibility, "but as open to as many people as they possibly can be".

With the world belatedly waking up to the impact of the three-year economic blockade of Gaza after last week's lethal commando raid on a pro-Palestinian flotilla, the summer games may seem like a footnote. But for UNRWA, both their undoubted importance to Gaza's parents and children, and the obstacles on the way to Sunday's launch, flow from the unique conditions of the Strip.

Mr Ging said after last month's attack that he would not be intimidated into forsaking the "huge responsibility to children that are suffering physically and psychologically in very difficult circumstances to provide them with a high quality recreation programme over the summer".

And he leaves no doubt as to what he means by the circumstances: "Blockade, occupation, no legitimate economy, a black market economy which is getting stronger and stronger, no prospect of getting a job." Not to mention undrinkable tap water, malfunctioning sewage and a ban on building materials which stops UNRWA constructing the 100 schools needed to end a near-universal two shift system in the existing ones. Circumstances which, he says, "cumulatively are quite unbearable for the entire population".

Ostensibly, it was exactly because girls like the three from Rimal prep would be taking part that the attack was launched in the first place. The attackers, who arrived at around 2.30am at the beachside camp south of Gaza City, handcuffed and hit the security guard Ibrahim Eliwa; took his mobile phone and ID card; and made him kneel with his face forward while they burned 20 plastic water tanks and slashed thousands of square feet of plastic and canvas sheeting.

When, before leaving, they tucked an envelope into Mr Eliwa's jacket pocket, it contained not only the ID card but a letter addressed to Mr Ging and two of his senior Palestinian staff declaring in Arabic: "We were shocked when we heard about establishing beach locations for girls at the age of puberty and adolescence aiming to attack Muslims' honour and morality. You have to know that we will give away our blood and life but we won't let this happen and will not let you malicious people beat us. So you either leave your plans or wait for your destiny." Just to reinforce the point, the gang also left three bullets behind for Mr Ging.

Mr Eliwa says the men were dressed in black, had radios, and were armed with AK-47s. He said he told the – Hamas-run – police that he thought the attackers were from Hamas. But whoever they were, it seems that Hamas security personnel, who at night mount a series of efficient checkpoints across the Strip, did not prevent their free passage to the camp. The Hamas de facto government condemned the attack publicly and police arrested an unspecified number of men for questioning, but have announced that anyone has been subsequently charged. However, there have been no repeats of the attack.

Major Ayman al Batniji, the police spokesman, claimed there were a number of groups capable of carrying it out. Acknowledging that "we have never witnessed any violations of Islamic law or custom" in the UN summer games. "So far we cannot point the finger at Hamas or any other faction," he said. And why had the police prevented civil society activists and members of the public subsequently protesting the attack from reaching the camp? "It was a political decision, not a police decision," the policeman explained. "Sometimes the police have to carry out political decisions they oppose."

In fact, the attack may also testify – however chillingly – to the popularity of the games. As a well organised, secular alternative, the summer games attract a much bigger attendance than parallel camps run by Hamas itself, that include Koranic instruction and military-style exercises.

Which may be why the oversubscribed UN games – Mr Ging says he could accommodate another 100,000 children if he had the funding – have been strongly, if verbally, attacked by some prominent Hamas figures, though not by the de facto government, which Mr Ging says has been "very careful" not to violate UNRWA's integrity. But Mr Ging has long argued that extremist trends in Gaza are the product of Gaza's isolation, "born of, but not justified by" circumstances that are "a breeding ground for a mindset which is negative, despairing, destructive, increasingly intolerant and will be more and more violent".

Which is why UNRWA schools teach "that there is no justification for violence and intolerance", seeks to instil shared universal values: respect, discipline, open-mindedness, tolerance and the understanding it is "illegal and wrong in every dimension" to fire rockets; and tries to elevate Gandhi, Mandela and Martin Luther King, as icons of the fight for human rights through "responsible behaviour".

Mr Ging acknowledges that some in Gaza "disagree with us on this". But he is convinced that the overwhelming "silent majority" of Gaza parents do not, and instead share those core universal values "that define us as civilised".

The flood of support to UNRWA from parents wanting the games to go ahead suggests he is right.

Mr Ging argues the message from Gaza is not only the misery and hardship inflicted by "the collective sanction of an innocent population" important though that is. It is also that "all is not bad here, all is not negative". For him the collective basketball dribbling and kite flying is a symbol of something bigger.

"There's a great future if we can turn the potential in a positive direction... the kids here are hugely talented and each world record achieved in these very difficult circumstances is evidence of that. So let's change the circumstances and let a thousand flowers bloom. Invest in these very talented kids and you won't be disappointed by the product."

UNRWA asked The Independent to change the names of the Rimal girls because of the sensitivities of their situation