With gun ownership falling, the US firearms lobby is targeting a new generation with dinky pump-action shotguns and junior shooting shows. But at what cost?

In the distance, there is snow on the ridges of the Rocky Mountains, but down here in the plains of Colorado there is only dust and sweat. In a layby just south of Denver, Texas Marshal is standing in the sweltering heat preparing for the showdown. He tips back his black felt bronco hat, pulls out his .45 Colt revolver and gives the barrel a slow, deliberate spin. Five brass bullets sink into the chambers and the gun goes back in its holster, ready to draw, his hand twitching expectantly above it.

His great adversary, Spud, is ready, too. He has a Ruger Vaquero single-action handgun at his side. As the signal is given, Spud moves first, pulling the gun up and cocking its trigger before Texas Marshal has barely started to move. There's a wrenching blast, Spud's barrel belches fire and the sweet, acrid smell of sulphur fills the air. Texas Marshal shoots second, but he's too late...

Texas Marshal emerges from the smoke without a scratch. They've been shooting at metal targets, not each other. But there's still the disappointment of losing to deal with, and that's not easy when you're only eight years old.

Texas Marshal and Spud, an old hand aged nine, are competing in the Colorado Cowboy Fast Draw championships – a modern rendition of the wild west one-on-one gunfights, minus the bloodshed. But though the competition is amicable, the guns are real – replicas of late-19th-century models, including the 1873 six-shooter made by Colt and ironically named the Peacemaker. As fast-draw enthusiasts like to remind you: "God made man, but Samuel Colt made them equal."

On the face of it, the fast-draw championships are no more than a simple test of the contestants' neuromuscular reactions. In truth, though, they are a form of worship, a gathering of the faithful in front of that peculiarly American altar, the gun. And amid this veneration, Texas Marshal and Spud have an important part to play. Spud, or Coby to give his real name, is the Billy the Kid world fast-draw champion in the eight to 12 years category. He can draw and hit the target in less than seven-tenths of a second. Blond-haired under a white cowboy hat, he was given his first gun at seven, when he started hunting jack rabbits in the fields in Idaho. He says he likes to shoot because, "I get to travel around the world – California, Texas, North Dakota."

Texas Marshal – or Dean – is a local Colorado boy. He also began aged seven, going after prairie dogs in his back yard. That's a ripe old age by some people's standards. Babalooey, the world champion in the girls' teenager class, was wielding her first firearm at five. She graduated from her dad's handguns to shotguns, then took up rifles to go dove hunting in the countryside around her home outside Phoenix, Arizona. "We make great dove nuggets," she says.

Her 14-year-old brother Pork Rind, looking remarkably like a barman in a western movie, dressed in a billowy shirt and brown derby hat, was just two when he pulled his first trigger. "We like to start them young in the American west," says his father, Gunslik Mick.

The National Rifle Association, the hugely powerful lobby that campaigns to uphold the second amendment right to bear arms, knows how crucial such young guns are to the gun-rights cause. Firearms manufacturers know it, too. As Handguns magazine put it, "Children are our salvation in the fight for liberty and the preservation of the shooting sports."

"We can win this battle, if we all try," proclaimed New England Firearms, a gun-maker, in an advert aimed at kids. "It will be an old-fashioned wrestling match for the hearts and minds of our children," echoed the NRA as it launched a campaign to "invest" in America's youth.

The metaphors might be extravagant, but the sentiment is accurate. America's gun interests do indeed have a struggle on their hands to engage the country's kids, for the simple reason that gun ownership is steadily declining. Over the last 30 years, the percentage of American households that have guns in the home has tailed off from a high of 54% in 1977 to 34.5% in 2006.

This dip can be attributed to a number of factors – from the slide in popularity of hunting to the end of military conscription and even the growth in single-parent homes that lack a gun-toting father figure. "Gun ownership is shrinking, and both the industry and the NRA know this," says Josh Sugarmann, director of the gun control campaign, the Violence Policy Center. "A primary aim is to find ways to increase the number of shooters in America, with the emphasis on children."

The methods deployed in this mission are many and various, beginning with Eddie Eagle, an avuncular cartoon character dreamed up by the NRA, who flaps around websites spreading safety tips. The NRA presents its feathered mascot as an educational tool for young kids who may come across a gun. But gun control advocates at the Violence Policy Center interpret the cartoon series as a marketing tool not dissimilar to the "health" information disseminated to children by tobacco companies.

The NRA also has its own young shooters' magazine called InSights. Its latest edition has a section called Something To Brag About that profiles Colton, aged four, who "just loves his Ruger Bearcat .22"; Alex, seven, who recently killed his first pheasant – "a trophy that most adults would be proud of"; and eight-year-old Sabastian Mann who shot a deer using what looks like an assault rifle. The magazine tells us it was, in fact, a Smith & Wesson M&P15 loaded with Nosler Partitions ammunition "to help seal the deal".

Lest that scarily grown-up-sounding firearm put anyone off, there is an entire corner of the gun-making industry dedicated to baby firearms. Take Mossberg's new model, the Half Pint. "This little, affordable .22 rifle is a great starter gun for taking on all kinds of assorted targets without breaking the bank," the blurb says. For those youngsters who want something a bit more robust, there is also the 500 Super Bantam, a pump-action shotgun designed for kids.

In fact, the number of models marketed unapologetically at children stretches to 42, including such endearing marques as the Chipmunk, Mini Bolt, Micro Hunter and Golden Boy. Girls have their own sub-genre of scaled-down rifles. InSights has a picture of 14-year-old Mackenzie Sipe sitting astride a Montana mule buck she has just killed using a pink rifle with purple titanium-coloured barrel. She calls it her "Princess Rifle".

For the most part, though, young shooters are brought up wielding adult guns. To get a sense of what's currently in fashion, I visit Caso's Gun-A-Rama, a vintage gun shop in New Jersey owned and run by Frank Caso. It has a plastic statue of Uncle Sam in the window holding the Stars and Stripes. On the wall is a signed photograph of gun-loving Charlton Heston, trophies of deer heads and pheasants, and a sobering police poster that says, "The misuse of handguns is a leading contributor to juvenile violence and fatalities."

There are 64 guns chained in the rack. At one end are the slender .22 rifles, which Caso says tend to be the young person's starter firearm of choice. At the other sit the shotguns. He pulls out a Remington 870, which, he says, is considered the "youth gun" because it has a shorter stock that makes it easier for smaller people to handle. It takes five shots, varying from birdshot to lead slugs and OO Buckshot – a larger pellet that Caso says can be used for deer hunting, going after bears or even crowd control.

I ask how old a child should be when they handle their first gun. "That's a parental decision," he replies. "It's not for me to say. I've two daughters and they've been around guns since the day they were born."

He bemoans the fact that young people are not coming into his shop in the numbers they used to, blaming computer games and television, and the dampening effect of politics. "Everything about guns is negative when it comes to politicians. I'm tired of fighting a losing battle over firearms." Then he launches into a diatribe about President Obama, accusing him of being anti-guns and desperate to get his hands on his second amendment rights.

In reality, since he entered the White House, the president has backed off an earlier promise to revive a ban on assault rifles. He has also allowed into law a new regulation that permits people to carry loaded guns into national parks. In July, a bill that would have allowed concealed guns to be carried in public places anywhere in the US came within a couple of votes of passing the Senate.

Indeed, America continues to have the most lax gun controls of any industrialised country in the world, with more than 200m guns in circulation. Four out of 10 of those are sold not by licensed firearm dealers such as Caso, but in gun shows and other locations where there is no requirement on the seller to go through any background check.

The results of such a lack of regulation are stark. In the last decade, some 29,000 children under 18 have been killed by firearms in the US, making it the second leading cause of death in this age bracket after car crashes. That's a rate 12 times higher than those in the other 25 industrialised nations put together.

Local papers carry gun death stories with a frequency that is emotionally numbing. "Two young children have been shot by their siblings in the space of 24 hours." "A two-year-old girl is in critical condition after being shot at a wedding reception." "An 11-year-old boy in Mississippi accidentally killed his nine-year-old brother with a shotgun blast after arguing about a video game."

"Boy accidentally kills himself with Uzi," was the Associated Press headline in October 2008. "An eight-year-old boy died after shooting himself in the head while firing an Uzi submachine gun under adult supervision at a gun fair." The Uzi was designed by the Israeli army in the 1940s and has been used by soldiers in wars around the globe. It can fire 600 rounds a minute. It is not, as a general rule, considered suitable for eight-year-olds. It recoiled, the barrel went up into the air and it discharged a round into the boy. One of the adult supervisors present was a firearms instructor who loaded the gun and handed it to the boy. The boy's father was also supervising; he was standing behind his son, holding him, when the bullet entered the right side of the boy's head.

Then there are the adults killed by children. Pamela Almli, 54, was walking in the mountains of Washington state last August when she was fatally shot by a 14-year-old boy out hunting with his brother, 16. He mistook her for a bear and hit her in the head from 120 metres. He was punished with 30 days in juvenile detention.

That this incident happened, tragic though it was, is not so surprising. Washington, along with six other states, has no minimum age for hunting alone. In almost half the states in the country, kids aged 12 or younger can hunt without any adult supervision.

The death of Pamela Almli was an accident. No such comfort in the case of Jordan Brown, 11, who in February killed his father's pregnant fiancee and then calmly went off to school. He shot her with a 20-gauge shotgun his father had given him as a present.

Nor in the events on 5 November last year in the small, rural town of St Johns in the deserts of Arizona. That story begins a few weeks earlier, when Vincent Romero, a construction worker, went with his second wife to visit the town's Catholic priest, the Rev John Paul Sauter. They had married only a month before and were having their first marital dispute, and wanted the priest to mediate. The row had been over Romero's eight-year-old son. Romero wanted to give the boy a gun and the stepmother was opposed to the idea.

Sauter tells me that it's not unusual for eight-year-olds in St Johns to have guns and go shooting. "It's not a wealthy town, and they do it partly to supplement their food income. They shoot and eat prairie dogs, which are very greasy, like a goose; and squirrels – squirrel enchiladas are delicious!"

But Sauter was himself anxious about giving the boy a gun, because he had learning difficulties and didn't seem ready to accept responsibility. "I said, you'd better wait till he is 12 and then put him on a course that teaches children how to hunt." But Romero, a keen hunter, resisted, saying there was no need for a course – he could teach the child himself. He would give him lots of hunting videos to watch, he said. And he went ahead and gave his son a .22-calibre rifle.

On the evening of 4 November, the boy had a row with his parents. They had already stopped him watching TV because he was failing to do his homework, and that night Romero was so angry he told the stepmother to spank the boy five times.

The next day, when Romero arrived home from work with a friend who rented a room in the house, the boy picked up the rifle his father had given him. He shot and killed the friend, then he killed his father. Both men were struck about five times, with the boy reloading after every shot.

At first the boy told police he had stumbled across the bodies and that he thought neighbours might have killed his father. But in an hour-long police interview he told a woman detective what had really happened. If you're feeling strong you can watch snippets of it on YouTube. Speaking in a cute Disney voice, the boy remembers the horrific events of that day as though describing buying an ice-cream. "I went upstairs and then I saw my dad and then I got the gun and then I fired it at my dad. He was on the ground and then I reloaded it."

The detective asks whether he was cross with his father. "The first time I was mad at him. But he was already shot, and I shot him again."

Then he goes on: "I think I shot my dad because he was suffering. I thought he was suffering. So I may have shot him. I didn't want him to suffer."

In a plea deal, the boy has admitted the killings and has been placed on a treatment programme for child offenders.

In most other parts of the world, it would be no extraordinary mental leap to correlate such killings with America's relaxed approach to gun control. After all, many eight-year-old boys get cross with their fathers, but they can't turn that anger into a bloodbath unless they have access to a gun. Thanks to the exalted position that the gun inhabits in the American psyche, however, that sort of logic has little purchase in the US, certainly in those parts of the country – the south and the west in particular – where gun ownership is high and shooting popular. Yet if you look at a map that plots where children have died by the gun in any one year, they are concentrated in precisely those same regions.

"Gun deaths and injuries in the US are directly related to gun availability," says Josh Sugarmann. "In other words, the areas where people relate most to the gun are killing themselves."

Back at the cowboy fast draw in Colorado, Texas Marshal is going for another head-to-head with Spud. His father, the handlebar mustachioed Nitro, is proudly cheering him on. "Just hit the target, buddy!" he shouts as the boy misses on his first draw. "Just hit the target!"

In between rounds, Nitro tells me how happy he is that his son is learning to be a shooter. It teaches him responsibility, as well as safety, which, he says, they take very seriously in cowboy fast draw.

But isn't it logical that the more guns there are in society, the more chance there is for tragedies to occur? "That may be how they think in England," Nitro says. "Here we don't blame the gun, we blame the human behind it." Besides, he goes on, "Do you think anyone would try violence on my boy if they knew he could hit them between the eyeballs at 20 paces?"

The kids line up for the last shot of the day. Texas Marshal's mouth clenches as he draws his revolver, cocks it and fires, this time on target. He puts the gun back in its holster and steps back. Nitro lifts him high off his feet in a huge bear hug.

"Good job, buddy," he says to his beaming son. "You done real good!"