A FEW weeks ago Helen Yovanna Mata, a 16-year-old Honduran girl, turned up at Corinto, a scruffy crossing on the border with Guatemala, with a backpack and a few papers. Two of the papers were death threats scribbled in scratchy ballpoint, another was a school document validating her story. One of the notes said: “We’re not kidding. You now have seven days [to leave]. We don’t want to hurt you, but you have to believe us. Death.” It was signed “M18”, the name of a violent Central American street gang. Honduran officials let her through to Guatemala, her first stop on an arduous journey north to the United States. No one knows if she got there.

Rising numbers of children are following in Helen’s footsteps. Corinto is abuzz with wiry, menacing men carrying dirty wads of banknotes who arrange for coyotillos—local kids turned people-smugglers—to lead migrants without passports through the subtropical hills into Guatemala. Since early this year, the vast majority of those migrants have been youngsters themselves, sometimes travelling alone, sometimes accompanied by their mothers. At night, when the coyotillos get to work, hordes of them walk up the back lanes, mothers cradling babies in arms, teenage girls with pink backpacks. They travel in such numbers that the village dogs howl.

Over 1,300 miles (2,090km) north of Corinto, on the Texan side of the Rio Grande, a lone man is fishing. The Mexican side, less than 100 yards away, is more festive: dozens of children are splashing in the shallow water and a party barge floats by, blaring music. A couple of US Border Patrol agents assess the scene. They spot several jet skis on the Mexican side as belonging to people-smugglers. And they point to a small group standing under a tree. “Black clothing in the summer?” says one. “Everyone else is in shorts, beach attire.”

The Rio Grande Valley is now the hottest spot for illegal crossings of the 2,000-mile border between the United States and Mexico. And an increasing number of border-jumpers are children travelling without their parents. The number of unaccompanied children caught crossing has surged to about 52,000 so far this fiscal year, which started in October, up from 15,700 in fiscal 2011. Most of them have come not from Mexico, but from Central America (see map). Of the youngsters caught so far this fiscal year, 15,000 are from Honduras, more than double last year’s number and five times the 2012 tally. (Plenty more get nabbed earlier in the journey: Fernando Lezama, the chief migration official in Corinto, says up to 5,000 unaccompanied Honduran kids have been deported from Mexico so far this year.)

The sudden influx of children into the United States has nearly overwhelmed the agencies that must deal with it. Detention facilities for children who cross the border illegally are horribly overcrowded. On June 5th Breitbart Texas, a conservative news site, published leaked photos showing dozens of children crammed into bare rooms. Barack Obama speaks of an “urgent humanitarian situation”.

The White House blames the influx on instability in Central America. A report by the UN High Commissioner for Refugees in March, based on interviews with around 300 Central American under-age detainees in the United States, put gang violence and domestic abuse high among the causes of flight—along with a desire to be reunited with relatives in America.

The stories of those back in Corinto support that explanation. Marisa Najar, a single mother travelling with her two children, ten and six, and a 15-year-old niece, Faviana, set out this month with 25 other Honduran friends and neighbours. Twice they reached Mexico before being deported, on one occasion riding “The Beast”, an infamous cargo train, part of the way from Arriaga, in southern Mexico. Faviana recalls the moment when gangsters on the train started counting the children. “They wanted to kidnap us or rape us,” she says matter-of-factly. The migrants hopped off and took a bus towards Mexico City, but were caught and sent home.

Faviana has left her unwed mother and six siblings behind because of street violence. She has not been to school for four years because, she says, gangs threaten to kill girls like her. Her uncle and aunt were recently murdered. Her mother is so poor, some days the family goes without food. Rape is a word she uses frequently; it happens all around her. But she hopes to reach the United States to go back to school. “I have always wanted to be a doctor,” she says. Her aunt, Ms Najar, has no home or job. She struggled to pay for books to keep her ten-year-old son, Zagdi, at school. When asked why he wants to go to America, Zagdi throws back his thin shoulders and says: “To work.”

Why now?

El Salvador, Honduras and Guatemala have had shockingly high murder rates for years, however. The reason so many of them have decided to leave at once is a widespread rumour that Mr Obama’s administration has relaxed the barriers against children—and their mothers if the children are young enough—entering the United States. A leaked border-agency memo based on interviews with 230 women and children apprehended in the Rio Grande Valley concluded that they had crossed the border mainly because they expected to be allowed to stay.

Migrants talk of a “permiso” (permit) to stay in the United States, although this may be a misunderstanding of the American immigration procedure in which many children are put in the care of family members while waiting for deportation hearings. Some Hondurans conspiratorially say they think America is preparing for war; that’s why they are letting more youngsters in. Others blame Facebook: it is easy for relatives in the United States to show the trappings of prosperity.

Who started these rumours is moot. The Obama administration blames unscrupulous people-smugglers trying to drum up business. What is clear is that misinformation runs rampant. Zagdi has convinced his group of fellow travellers that there will be permisos until October 1st, saying he heard it on television. No one sees fit to disbelieve him, or check his facts.

On June 20th the White House dispatched Vice-President Joe Biden to Central America to squash the rumours. Granted, in 2012 Mr Obama ordered that many illegal immigrants brought to America as children should have their deportation proceedings deferred. But that applies only to those who arrived before 2007. Mr Biden stressed that there was no “open-arms” policy. “We’re going to send the vast majority of you back,” he said.

Like many rumours, however, this crop has some grounding in truth. America deported 370,000 people in fiscal 2013, a huge increase on earlier years. Yet since there are an estimated 11.7m illegal immigrants in America, even a deportation machine running at high speed must be selective. The Immigration and Customs Enforcement agency (ICE) prioritises the removal of adults with criminal records rather than children with none.

Whereas the United States is allowed rapidly to send illegal Mexican child migrants back across the border, it is required to treat those from Central America differently. Under the Trafficking Victims Protection Reauthorisation Act of 2008, moreover, border agents cannot hold children for more than 72 hours. They must be given a court hearing before they are either deported or allowed to stay. Since there are around 5,000 immigration cases pending for every qualified judge, that can take years. While the child migrants wait, around 90% go to stay with a relative already in the United States, says the Migration Policy Institute (MPI), a think-tank.

They may start school, make friends and perhaps learn to swing a baseball bat. Those who don’t have family in the United States are cared for by foster families or put into residential facilities, which are already full. In Lawrenceville, a 1,400-strong town in Virginia, the federal government is trying to convert a disused university campus into accommodation for 500 children.

The customers at Crazy Joe’s, a beer garden in the Texan border town of Mission, have seen the changes in migration close up. In previous years, migrants and smugglers were usually young men with backpacks, darting through the brush to the safety of a waiting car. “Those ones hide, and they run,” says Sarah Garcia, the owner. The new ones do the opposite. For the past three weeks, migrants have been turning up at Crazy Joe’s every other day. None of them was trying to avoid being spotted. A group of boys, all claiming to be 16 or 17 years old, asked Ms Garcia for directions to Austin, to Virginia, to New York. A family with a baby accepted some ibuprofen and nappies. Most of the new arrivals, Ms Garcia says, want her to call the Border Patrol.

People-smugglers have changed their behaviour, too. They used to charge $3,000 per adult for three attempts at crossing. As the chances of getting an adult across have fallen because of tighter controls, the odds of getting a child in (for the same $3,000 payment) have stayed the same. In some cases children have floated across the Rio Grande on rafts in full view of agents on the banks, says Doris Meissner of MPI.

Draconian policies, perverse effects

If the explanation for the influx is complicated, the politics of it are brutally straightforward. Republicans blame the president. “Children are pushed into the hands of criminals,” fumed Ted Cruz, a Texan senator, “because the Obama administration has made it clear to the world that any child who arrives, regardless of whether they are granted formal legal status, will be permitted to stay.” Mr Obama, he added, showed “an outright refusal to enforce the law”. John Boehner, the Speaker of the Republican-controlled House of Representatives, has called for the National Guard to be sent to the border, though what they would do there is not clear.

It is hard to see what will reverse the flow. The White House has promised more help to Central American countries and more immigration judges, but not much else. As elections approach, hardliners will call for yet more spending on border security, even though the militarisation of the border may have contributed to the crisis.

The surge in child migrants comes as the total number of people crossing the south-western border illegally has fallen sharply. In fiscal 2000, 1.6m people were apprehended by border-patrol agents. By 2013 that number had fallen to 415,000. This partly reflects America’s economic doldrums and greater opportunities in Mexico. But it is also harder to get in than before. A study in 2008 found that a would-be migrant who kept trying was almost certain to succeed eventually, so illegal immigrants would regularly go home to see their families, secure in the knowledge that they would be able to return. Now they tend to stay put. Stricter border enforcement thus keeps families apart, and gives migrant parents a powerful incentive to send for their kids.

In this environment, however, the prospects for comprehensive immigration reform, which might allow more temporary workers to move back and forth across the border, are not looking good. The Obama administration’s messages of discouragement may put some migrants off. But Ms Najar, her family and friends are all the more eager to set off again before the door shuts for good. “We have faith that we will make it. If we don’t, it is God’s will that we should remain in this hell of a country.”