By Mark Potter, NBC News correspondent

COLUMBUS, NEW MEXICO -- In reporting tonight's Nightly News story on how the vicious war between drug cartels and police throughout Mexico is affecting U.S. border towns, we came across some disturbing evidence that adults aren't the only victims.

In Columbus, New Mexico, some 400 American-born children, who actually live across the border in Palomas, Mexico, come to the Port of Entry most mornings to clear immigration, board buses and then head off to school on the U.S. side.

In talking to some of those elementary and middle school children, we found out that they are quite aware of the dangers that traffickers have brought to their tiny town. So far this year, a drug-related turf war in Palomas has claimed some 40 lives. Throughout Mexico, that war has caused about 4,000 deaths since the start of last year, with many of the victims being top law enforcement officials.

Talking with the children, we heard one boy describe a gun battle near his home in Palomas. "They start shooting everywhere and you don't know where to go," he said. He added that while in the relative safety of the American side of the border he is still concerned about the dangers back home. "When I walk from there over here I worry about my parents," he said. "When I'm coming back I worry about myself."

Many of the children talked casually about the killings and the weapons involved. "You can hear by the sound, AK-47," one said, describing the traffickers' rifle of choice. And a boy who lives near the border fence said, "All the time you can hear shootings downtown, drive-bys, too. Everywhere you could hear the shootings. It's, uh, people dead."

Some of the girls we met had similar stories. One stunned us by saying, "It has happened around my house, 'cuz people who are involved live there."

When asked if they are afraid, many of the children said they were. But others said they had just become numb to the violence. "At first, when it all started, it was kind of scary, but then you have to get used to it," a young girl told us.

When asked if he had actually seen a shooting, a boy said firmly, "I haven't seen that and I don't wish to see it, 'cuz if you see something like that they can kill you, 'cuz they want no witnesses."

A life-saving thought perhaps, but surely too much for a little school-kid to have to know.

photo by NBC's Stephanie Himango