The humanising experiences of middle-aged Palestinians and Israelis who had contact in everyday situations have faded away, replaced by confrontation, trauma and hatred

Abu Nizar's father had good things to say about the Israelis he knew. "He told me they were decent to him when he worked there. He did whatever work he could find with them. Construction, the fields. He had a good opinion of them. They treated him well," the son said.

Abu Nizar has never met an Israeli who wasn't carrying a gun. Unlike his father, who travelled across the Jewish state to work different jobs, the 24-year-old has not spent a day outside the Gaza Strip, other than a brief sortie into Egypt. He is not interested in knowing Israelis. He just wants them to go away. And he is willing to fight them to make that happen.

"Myself, I don't want to meet them. They are all occupiers, an enemy," said Abu Nizar sitting among other fighters from the Al-Aqsa Martyrs Brigade in Beach Camp, a Gaza refugee camp. He said his unit had fired dozens of rockets from Gaza in the recent battles.

One of the results of years of conflict is a generation of young adults on both sides who rarely meet each other except at the point of a weapon. The humanising experiences of middle-aged Palestinians and Israelis who had contact in everyday situations – such as Palestinians working in Israel who often learned Hebrew, or Israelis taking cars for repair by Palestinian mechanics or shopping in Arab markets – faded away with two intifadas and an ever more brutal occupation.

Abu Nizar and others of his generation have not only never met an Israeli except in confrontation but grew up with the trauma of living in neighbourhoods that felt like perpetual combat zones. They in turn are raising a generation of sons and daughters enduring life under periodic barrages of rockets and shells, and perpetual siege, and developing their own perceptions of Israelis as a dehumanised enemy. "We didn't have a normal childhood at all. The Israelis created a whole generation that hates them. They are idiots. This last war has doubled, trebled the hatred from kids today," said Abu Nizar, a small, slight man with a neatly trimmed beard. "My three-year-old is always asking me: why is this? What's going on? Why are there rocket blasts? I tried to tell him what's happening and now he hates Israel."

Another fighter, Abu Jindal, speaks up. "The Israelis have always killed children in Gaza. They came here to kill children during this [latest] war. Our children see it," he said.

Israelis often tell themselves that Palestinian children are brought up on their mother's knees to despise Jews, and as they grow up the hatred is piled on in schools and mosques. Some of that is true some of the time, but it is also a convenience for Israelis to absolve themselves of responsibility for why each generation of Palestinians seems more militant and more violent.

The generation of young adults in Gaza that, like Abu Nizar, has taken up arms was also shaped by a childhood marked by fear of Israeli guns, rockets and tanks enforcing occupation and taking territory for Jewish settlements. They saw people their own age killed and maimed by indiscriminate shooting. And they watched their parents helpless in the face of the humiliations of occupation.

As happens in so many conflicts, Palestinian children were raised to honour the warriors and the dead. They worshipped "martyrs", whether they were suicide bombers who killed Israelis on buses in Jerusalem, armed men fighting Israeli soldiers, or the children shot at their school desks in Gaza by Israeli gunfire.

In 2004, Usama Freona, a psychologist at the UN clinic in Rafah, described to me the impact of perpetual conflict on children. At the time, Rafah and neighbouring Khan Yunis were among the most dangerous places in the Gaza Strip because of the adjacent Jewish settlements.

The Israeli army declared the whole area a war zone which, it said, justified firing weapons into residential areas. Barely a night passed without the machine gun fire that shredded homes and forced families to sleep in an inner room behind bricked-up windows or a second wall.

"The levels of violence children are exposed to is horrific," Freona said. "We work in a lot of schools to treat the children. In the one next to Kfar Darom [a Jewish settlement in Gaza at the time], all the children are suffering from post-traumatic stress disorder. Most of them were crying and shaking when they were speaking about their experiences."

Three years ago Gaza's leading child psychiatrist, Dr Abdel Aziz Mousa Thabet, said in an interview with the Guardian that the traumatising effect of violence on children was shaping a generation itself ready to use violence. He said a 20-year study showed that about 65% of young people in the Gaza Strip suffered from post-traumatic stress disorder, with a profound effect on enclave's future.

"They become fighters. I warned about this 15 years ago, that in 15 years these traumatised children will be more aggressive, they will want to fight, there will be more violence in the community," he said. "So now we will have another generation of more aggressive behaviour. They will go to more extremes because they have no future. This is a problem. I've been warning people of this but nobody was listening. It's a cycle of aggression."

Abu Nizar's experience fits the pattern. In the 2000s, Israeli attacks on Beach Camp and Jabaliya were routine. A cousin was killed. So were other people he knew. But even before that, he had encounters with Israeli troops.

"I used to see the soldiers when I was small," he said. "I used to throw stones at them. I remember the occupation. We were the kids of the stones. I was beaten. There was a curfew. I was caught and beaten up. I was seven years old," he said.

Abu Nizar watched how Israeli troops treated the men in his family: "They arrested my father. They arrested my uncles. The Israelis would come at night. They called all the men into the street and put them in an open area and beat them. They humiliated them. This created the hatred of the occupation."

The humiliation of Palestinian men in raids and at checkpoints, sometimes by young female Israeli soldiers, could have a powerful effect on boys and routinely continues to this day in the West Bank. Freona described how boys lost respect for their fathers because they were helpless to stand up to the soldiers. Instead children would look to the armed men with admiration because they represented resistance.

Abu Nizar picked up a gun for the Al-Aqsa Martyrs Brigades, an offshoot of Yasser Arafat's Fatah movement, in 2005, aged 17.

At the time, Gaza was still partially occupied and under regular Israeli bombardment and ground attack. That first year he lost schoolfriends to an Israeli attack. "There was an incursion in Jabaliya. My friends were killed by an Apache helicopter," he said.

Now Abu Nizar is quite frank that he regards himself, and his role as fighter, as a product of a childhood in a combat zone. It is how he comes to be at ease with the fact that the rockets he fires into Israel may be causing civilian casualties there, such as the three who died, along with a soldier, from rockets fired from Gaza in recent round of fighting. For him there is no such thing as a civilian on the other side.

"The [Israeli] civilian is a soldier. The men who employed my father serves in the army. They come here to kill and then go back home, no problem," he said. "Anyway, we know how Israelis regard us. They want to kill us all."

Abu Nizar and Abu Jindal both have children of their own now who are being shaped by the conflict around them. The eldest of Abu Jandel's four daughters is nine. "She is always afraid but at the same time she wants to do something, something against Israel," he said.

Abu Nizar has two boys, aged three and 11 months. How would he feel if, in a few years, his eldest son put his life on the line to confront Israel?

The stock answer from many Palestinians to that question is that they would gladly have their children die for the cause – more often a statement of solidarity for the cause than a hope. But Abu Nizar hesitates.

"When I was young, it was just stones back then. Now it's rockets," he said. "When he grows up he will take his own decision. I don't know if it will be the same. The end of Israel is getting closer."

As for Abu Nizar's father, the young fighter says his parent's views of Israelis have changed. "My father experienced the crimes of the Israelis. The picture of Israel has changed in front of his eyes. I was talking to my father last week. For him, the real face of Israel has been exposed," he said.