With a rolled-up mat slung over his back, Honduran 14-year-old Kevin climbs aboard a Mexican freight train for a 1,450-mile (2,330-km) journey to the U.S. border -- a perilous ride spotlighted by a new documentary.

What I've always dreamed of was to be in the United States. Most of the children in Honduras, they grow up with that idea, Kevin says in Which Way Home, a film that will be broadcast on U.S. cable network HBO Monday.

Every year thousands of Central American migrants travel on Mexican freight trains toward the U.S. border, and about 5 percent of those are children traveling without a parent, train officials told documentary director Rebecca Cammisa.

Roughly 12 million illegal immigrants live and work in the United States, some 2 million of them from poverty-hit and disaster-prone countries in Central America.

The truth is my mother is really poor. The money she makes is barely enough to feed us, Kevin, who is traveling with his 13-year-old friend Fito, says in the film. In my life I would like to be able to help her and be able to buy her a house.

Which Way Home follows Kevin, Fito and several other children as they make the journey north, risking being robbed, raped, beaten or killed by criminals preying on the vulnerable migrants, or being killed or maimed if they fall off the train.

For migrants who are trying to get through Mexico to get to the United States the situation is incredibly dehumanizing, Cammisa told Reuters in an interview. (At a detention center) a young boy came through and just collapsed in front of us.

He was completely and utterly devastated, she said. He had been traveling with his brother and his sister. All three of them were trying to get to the United States. His sister was gang-raped and his brother was shot to death in front of him.

DANGER BEYOND BORDER

U.S. officials told Cammisa that about 100,000 children are detained annually for illegally entering the United States.

Children featured in Which Way Home said they were trying to get to the United States to reunite with a parent or create a better life for themselves. Some said they hoped to be adopted by a U.S. family.

But while the journey through Mexico has dangers, it doesn't end at the U.S. border where migrants often are faced with vast deserts. Which Way Home features the families of two teen-aged cousins -- aged 13 and 16 -- who made it to the United States but died from exposure in the Arizona desert.

The immigration issue evokes strong emotions on both sides of the debate in the United States. President Barack Obama has said he expects Congress to overhaul the country's immigration system by early next year.

In June Obama tapped Homeland Security Secretary Janet Napolitano to meet regularly with lawmakers to work through a number of controversial issues, such as how to handle the illegal immigrants already in the United States and how to prevent future illegal immigration.

Cammisa said she first read about the migrant train trips in a newspaper and has spent more than six years working on the film, using grants from Robert Redford's Sundance Institute, HBO and a Fulbright Scholarship before actor John Malkovich's production company Mr Mudd took on the documentary.

I'm hoping that people will see this film and it will maybe deepen their understanding, help create a more compassionate view, Cammisa said. I'm hoping that this film can be used as a tool pushing positive immigration reform.

People are coming, people are desperate, they want a better life, Cammisa said. There has to be a practical sensible approach to understanding that people need to work here, we need workers here, make it legal and humane.