Maddalena Chiarenza never quite knows what state the children will be in when they arrive at her door. She has seen terrible injuries. Black eyes, missing teeth. A broken jaw.

“They suffer such regular violence,” says Chiarenza, whose Brussels-based NGO, SOS Jeune, cares for unaccompanied Moroccan and Algerian children.

A short walk from the NGO’s office near the Eurostar terminal, ragged groups of north African children are a common sight. Some walk through the streets like zombies, after being fed Rivotril, a potent benzodiazepine.

Chiarenza says that other than a handful of NGOs such as SOS Jeune, these children have few friends. Nobody wants to take responsibility for their care.

Some of the children the NGO has cared for have since died; through sickness, murder or suicide; Chiarenza says at least five in the past three years. Another 23 children it has had contact with are in prison, some on drug offences.

On the surface, the plight of these unaccompanied child migrants, and hundreds of others like them throughout Europe, is a testament to the failure of governments across the continent to provide help and assistance to the most vulnerable victims of the global migration crisis.

Dig deeper and these children tell a different story, an untold narrative of Europe’s growing addiction to chemical formula C₁₇H₂₁NO₄ – cocaine.

A Guardian investigation has found that hundreds, if not thousands, of African children have been trafficked into Europe’s booming cocaine trade, small cogs in a £10bn criminal industry that is transporting vast quantities of the drug from the Andean rainforests to increasing numbers of customers across the continent.

Police intelligence identifies an “unlimited” supply of vulnerable child labour trafficked from north Africa to work for Europe’s top-tier cocaine networks.

In March, senior police officers convened a secret meeting in Brussels. Present were officers from 25 EU countries along with the UK, Europol, the EU border force, Frontex, the UN refugee agency and the European Commission.

On the agenda: the exploitation of unaccompanied African children by powerful international drug syndicates based in western Europe.

“We have evidence that these foreign minors are exploited in large numbers in the EU by OCGs [organised crime groups] involved in drug trafficking,” says a police source who was present.

The phenomenon, police say, is on an industrial scale. Investigators looking into the mass recruitment of minors by cocaine networks in Belgium quickly realised their modus operandi was being replicated throughout Europe.

A Belgian police document chronicles a recent briefing by European officers investigating organised crime and human trafficking: “Belgium, the Netherlands, Spain and France presented several concrete cases of the exploitation of hundreds of north African minors, recruited by drug trafficking networks to sell narcotics.”

The cocaine networks are particularly brutal, say police. Children are told to sell a set quota of drugs or risk being gang raped. Videos confirm the threat is real. Others are forced to have sex with adults to secure a place in a squat. A report for Dutch justice officials found such “networks” ruled by savagery. It says: “The [networks] force them to do things; many of the boys have been raped and filmed when being raped.”

Retribution is guaranteed. One child caught by Brussels police selling drugs was found two days later covered in bruises. A punishment beating.

Some have fled Belgium; terrified they will be killed because they owed money from dealing.

A number are converted into child soldiers: proxies ordered to attack rival drug gangs, usually with knives.

“We find them with horrific injuries, deep blade wounds that they try to treat themselves,” says a Brussels social worker.

The latest Europol intelligence confirms the “abusive” hiring of children by such networks to target rivals. It says: “They recruit minors for the commission of violent attacks to intimidate non-collaborative actors.”

One of Europe’s most senior officers investigating the exploitation of such children warns that the threat is most pronounced for minors from two African countries.

A veteran of 30 years experience, Belgian judicial commissioner Eric Garbar says: “Moroccan and Algerian minors are particularly vulnerable and are most commonly exploited by OCGs involved in criminal activities like drug trafficking.”

Concern has recently surfaced in London. Meetings involving police and child protection officials are attempting to establish the criminal network behind a number of Moroccan and Algerian children found horribly disfigured. The youngsters, say sources, were tortured.

Youssef knew it would be different, but arriving in Europe was like landing on another planet. “You don’t know the language, the values​, the customs – or anybody. It’s a big shock.” Having fled the Moroccan city of Salé and an abusive father, Youssef was vulnerable when, aged 15, he reached Spain and headed to Brussels.

Belgium’s children’s rights commissioner Caroline Vrijens describes boys such as Youssef as “the most vulnerable” minors on the continent.

Drug gangs would concur. “Criminals in Europe approached me but I always refused,” says Youssef. Others were less resolute. Some of Youssef’s friends have simply disappeared.

“They are at the mercy of organised crime groups,” states a Belgian police document sent to Europol last December, adding: “… to whom they turn like shipwrecked sailors drawn by the reassuring light of a lighthouse”.

The brightest, biggest, lighthouse belongs to a Moroccan cocaine network colloquially known as the “Mocro Maffia”. It controls much of the turf around the Brussels Eurostar terminal. More germane is its control of Europe’s second largest container port, 30 miles north.

Antwerp has become the continent’s main gateway for cocaine shipped from South America, hidden among the 12m containers passing through each year.

Last year, authorities seized a record 116 tonnes of cocaine at the port. A lot still gets through: according to reports, just 1% or 2% of containers coming into Antwerp are searched by officials. And each tonne that does make it past the authorities, tightens the Mocro Maffia’s grip and furthers its project to meet Europe’s growing demand for the drug.

Analysts say that Europe’s increasingly powerful cocaine gangs, such as the Mocro Maffia, are now working directly with the South American cartels to encourage cocaine production to reach record levels.

The sheer volume of the cocaine pipeline from South America to Europe is keeping prices low and quality high. Compared with the 1990s, the street price of cocaine is equivalent to £20 a gram.

“It’s a more affordable, purer product than 20, 30 years ago,” said Tim Surmont, an analyst at the European Monitoring Centre for Drugs and Drug Addiction.

Consumers have responded accordingly: four times more Europeans use cocaine than two decades ago.

But market growth also needs manpower. The Mocro Maffia were not sluggish to appreciate that undocumented, unaccompanied children such as Youssef make ideal, cheap and disposable street-drug sellers.

A recent Belgian police report, shared with Europol, cites the “Mokkro [sic] Maffia” as a structured criminal network that “no longer hesitates to exploit minors to enrich themselves”.

The pool of labour is significant. Last year police referred 623 unaccompanied children from Morocco and Algeria to Brussels’ safeguarding service. Others melt away, never to be found.

Tijana Popovic of Child Focus in Brussels recorded 332 “worrying” disappearances of unaccompanied minors in Brussels last year, including a cohort aged 11 and 12.

Garbar, in a police report, states that thousands of unaccompanied children enter Europe each year and “disappear without any traceable trail”.

He adds: “Many of them are ‘captured’ by criminal circles.”

Aside from Brussels, many vanish in Paris. Last year, police disrupted a large-scale drug network in the Barbès area that exploited Algerian children.

More recently, London has emerged as a source of concern, with police and child protection experts meeting to discuss an alarming new trend. Highly vulnerable Moroccan children, seemingly controlled by criminals, have been found in at least four north London boroughs.

During February and March, British Transport Police found nine Moroccan or Algerian children who required urgent safeguarding. Five were found on London’s rail or underground network.

Det Supt Arlene Wilson says: “We identified children and vulnerable people on the railway network who we consider to be victims of exploitation and modern-day slavery.”

Police investigating the issue have, say sources, raided an address in Finsbury Park, north London. The authorities were forced to move quickly. Not only were the children vulnerable: they were being abused.

“The young people identified in the UK seemed to have quite severe wounds; indicators they’ve been subjected to high levels of violence,” says a child protection source. “Violent assault as a method of control.”

Amin turns, squinting in the sun, his face crisscrossed with scars he refuses to discuss. Behind him, a six-metre fence separates Morocco from the Spanish enclave of Melilla. For three years, like hundreds of other unaccompanied minors, Amin has survived by selling tissues to dock-workers in the port of Beni Ansar, playing cat and mouse while evading authorities keen to eject him.

Over the fence lies Europe. Freedom. Soon, surely, he will scale the fence?

“I want to help my family, go to Europe. I want to change my life,” says the 13-year-old, who left home to search for work after his father died.

Youssef passed through this way too, climbing the fence, lying low in a rescue boat bound for Spain. Most hide in trucks, often exploiting the chaos of events such as the Paris-Dakar rally. A number are trafficked direct to cocaine networks based in cities such as Brussels, say police.

Criminal syndicates are adept at using social media to lure children such as Youssef and Amin. Platforms host harraga channels linked to drug networks promising a better life in Europe.

Harraga means “to burn” in Arabic, a nod to the destruction of personal documents to avoid identification once in Europe. Children such as Amin call themselves harragas – burners.

Police say the Mocro Maffia is in no danger of running out of burners.

“The Mocro Maffia understand that in their country of origin they have at their disposal unlimited human resources. What we have in the EU is an unstoppable low-cost human resource from Africa,” says Garbar.

At some stage, officers expect the source of young, cheap labour from Africa to widen further, increasingly exploiting children from states such as Sudan. Cocaine networks have been quick to capitalise on the tumult in Afghanistan. During the Brussels meeting in March, police shared evidence of Afghan children as young as 12 being trafficked en masse into Europe’s cocaine capital, Antwerp.

Back in Brussels, armed police are herding young Moroccans away from the Eurostar terminal. June’s European elections are close: semi comatose children peddling coke is not a great look for the capital of EU politics.

A separate police operation will soon be announced to tackle the trafficking of African children into Europe’s cocaine cartels.

More broadly, a change in policing mindset is required, says Garbar. Arresting the child street dealers makes zero difference. The district surrounding the Eurostar has seen 2,000 drug-related arrests over the past six months without any apparent impact on cocaine supply.

Youssef urges a humane solution, one that harnesses the children’s durability.

“To live and survive life on the street you have to be strong. They need to be seen as human, given a chance away from crime.”

Youssef is proof they can prosper. Now 25, he has lived in Belgium for six years and works for the Red Cross.

Garbar warns that failure to assimilate such vulnerable children will end with Europe paying a high price. Today’s 12-year-old street dealers are tomorrow’s narco-bosses.

“Once they are adults, these young people will be a threat to our societies. They are ill-adapted to our lifestyles and have been unable to benefit from protection and appropriate care by our states.

“These young people will continue their criminal activities and grow in power. If we don’t act against this phenomenon then, in 10, 15, 20 years, we are going to face one of our most important problems.”

*Some names have been changed