As young as 10 years old, they live rough in their dozens, waiting for a chance to stow away on a boat across the Mediterranean sea.
Here in the Spanish territory of Melilla, they flock from neighbouring Morocco by sea in flimsy dinghies, by road crammed under the seats of cars, or on foot, dodging guards to scramble over the border fence.
Some of the youngest, underage and unaccompanied, camp out by a high breakwater running to the sea, where they have set up shelters of cardboard boxes between the cement blocks of the dyke.
"I have been here for three weeks. I am going to climb on board a truck" bound for Europe, says Mounen Fannan, a 17-year-old from Morocco.
In his home city of Fez "there is nothing to do. In Europe, there's a much better chance of getting ahead."
As unaccompanied minors, Mounen and others like him -- the youngest of their group is aged 10 -- are not allowed to stay in the Melilla's state-run reception centre, where children must be accompanied by their parents.
Some have stayed at the local reception centre for minors but say they ran away because they were mistreated. So they camp by the breakwater.
Among them are Moroccans, Algerians and some from Syria, displaced by that country's civil war, says Jose Palazon of Prodein, an aid group.
"They are totally outside the system. They come here intending to get on a boat to get to reception centres on the mainland, which are said to be better," he said.
"They are children and most of them have family problems. Many come because they are running away from abuse, because their parents have died or the parents can't afford to feed them."
Crossroads of illegal migration
To get out of Melilla, "they climb over this sea wall and land in the port. Then they try to hide on board a truck, the truck gets on a ship and they turn up in Malaga or Almeria" on the coast of southern Spain, Palazon added.
"It is very difficult, but they manage. Each week there are about four or five who leave and do not come back."
Metres from the dyke, a Spanish police boat patrols at sea, without drawing near where the youngsters are camped.
"There's not much that can be done," said Lieutenant Juan Antonio Martin Rivera, a local police spokesman.
"It is a delicate situation. It will have to be tackled in a multidisciplinary way. The city's social services, the juvenile courts and the security forces will have to work together to see how to ease this problem."
Melilla, which has 80,000 inhabitants, is the crossroads for migrants who try to slip through to Europe.
Charges at the six-metre (19-foot) fence by crowds of migrants make regular headlines.
"The ones who scale the wall draw the most media attention, but immigration has many faces," said Martin.
"The two main ways are to enter by sea in a vessel or by swimming, and in false bottoms in vehicles. The trafficking gangs put the immigrants there in dreadful, disastrous conditions. They put their lives at risk."
Those two methods are used by migrants from sub-Saharan Africa, while those from neighbouring Algeria pass the border with forged Moroccan identity papers, he said.
By boat, not knowing how to swim
Some 35,000 people and up to 7,000 cars cross into Melilla at its main border post every day under a visa-waiver agreement between Spain and Morocco for people living in the area.
In the queue, Spanish police search the boots and bodywork of vehicles. They recently found a girl of 16 and a boy of 17 hidden in a Mercedes, which now stands by partly dismantled.
"Traffickers charge between two and four thousand euros ($5,500) for every immigrant they hide in the false bottom of a car," said Martin.
"For the boats, they charge 1,500 euros per person and lately they have even been putting women and children on them. A lot of them don't know how to swim."
Many African migrants have died while sailing in flimsy vessels in the Mediterranean over recent years.
Those that make it to Melilla look for a chance to cross to Europe, by boat or hidden in trucks or shipping containers.
"They put themselves in some unbelievable places," Martin added. "We've seen cases of people in bags of radioactive material."