What are border crossings like for trains? I've always wondered because it seems like it would be a gaping hole in "border security" unless they x-ray every train car.
This has been happening already for at least a decade.
There is an excellent but heartbreaking documentary of kids riding the trains by themselves from Central America to the Mexico-US border in hopes of migrating to the US based solely off what they learned from Hollywood propaganda. It's called Which Way Home. I highly recommend it.