The first time Emanuele Sibillo was arrested he was 15: the police raided his house in the Forcella district in Naples while he was trying to get rid of two guns.

Sibillo was in and out of prison throughout the following few years. Among the young inmates, he stood out for his ability to command respect and for reading books and newspapers.

When he turned 18 in 2013, he prepared for the next big step: rebelling against the old Camorra clans of the Neapolitan mafia to take over the whole city.

Since the early 2000s, Italian authorities have arrested hundreds of Camorra bosses and, with the old mobsters either murdered or behind bars, children and young adults such as Sibillo have begun taking their place.

The phenomenon was the subject of La Paranza Dei Bambini, a 2016 novel by the Italian writer Roberto Saviano, whose bestselling non-fiction work Gomorrah, published a decade earlier, had shone a light on the Camorra and resulted in him being granted round-the-clock police protection.

Paranza translates as a small fishing boat but, in Camorra lingo, it refers to a criminal group led by youngsters or small fish. Saviano refers to these children – many of whom carry 9mm revolvers by the age of 15 or 16 – as piranhas.

La Paranza dei Bambini was made into a film – The Piranhas, directed by Claudio Giovannesi – which won a Silver Bear best screenplay award at this year’s Berlin film festival. The book and film chart the story of Nicola, a boy from the poor Rione Sanità district of Naples, who choses to enter the “system”, as the Camorra is known.

Saviano said: “Crime [in neighbourhoods such as Rione Sanità] becomes the only way to make it, the only way to get money, power, respect. It’s not about being unable to wait for your moment. These guys know their moment will never come [otherwise].’’

Moreover, according to Saviano, “criminal organisations seem to be the only ones, always, to notice the existence of these children and enlist them”.

In Naples, the trend is all the more alarming because the Camorra’s structure is horizontal, not hierarchical like Italy’s other main mafia outfits, the Cosa Nostra and ’Ndrangheta. The result is a neverending state of war among Camorra clans for territorial control, a war now taken over by the paranze.

With generational change has come a change in style. Whereas the older mafia bosses often operated out of the limelight, observing omertà - the code of silence – today’s criminals broadcast their exploits on social media, where they pose in designer clothes, clutching €200 bottles of champagne. They wear hipster-style beards and race through the alleyways of Naples on scooters like packs of wild dogs. And they shoot.

One man was shot in 2014 simply because he asked for a cigarette. An Indian man took a bullet in the chest in 2013 when two boys were “testing their gun”. One young mafia member placed under surveillance was overheard on a wiretap screaming with joy about a new gun. “I have a chrome 357 Magnum with a rubber grip, just like Al Capone’s!,” he said.

Last summer, the court of appeal in Naples sentenced 42 members of two paranze from the Forcella and Decumani districts to a combined 500 years in prison.

Giovannesi said: “We wanted to tell the story of these lives. Let’s not forget, these are just teenagers.” While working on the screenplay, he was influenced by great works of literature on adolescence, such as Lord of the Flies, he said. “All these books touch on the subtle contradiction between playing games and raging war.”

Saviano said the the existence of the paranze was partly a product of poor social policies and the failure of state institutions including schools.

Giovanni Melillo, the chief prosecutor in Naples, said the gangs were widespread in the city, where young people are recruited based on their ability for violence.

“The clans delegate to them the business of drug dealing and racketeering – a worrying phenomenon but marginal compared to the [traditional] clan operations of infiltrating public administrations and financial markets,” Melillo said. “But when the paranze go overboard with raids, the [remaining] older bosses intervene in order to keep the peace.”

In 2014, Sibillo was 18 and considered the baby godfather of the Forcella district. A year later, he was dead, the victim of an attack by members of a rival clan.