Available in bright blues and hot pinks, rifles for kids sell in their thousands in America. They look like toys – but they’re lethal. An-Sofie Kesteleyn travelled to photograph this juvenile army

In May last year, a two-year-old girl was shot dead by her five-year-old brother with a small rifle made specifically for children. The accidental shooting happened in Cumberland County, Kentucky, when the boy was playing with a gun purchased from a company in Pennsylvania called Keystone Sporting Arms, which, in 2008, produced around 80,000 rifles for children. The guns, which sell under the model names Cricket and Chipmunk, were originally advertised on a "Kid's Corner" on the company's website (it has since been removed), which showed children firing them at rifle ranges and on hunting trips. The guns are produced in bright blue, pink and rainbow colours and marketed like toys, under the tag line "My First Rifle".

Benjamin, aged 7, from Louisiana

When the photographer An-Sofie Kesteleyn read about the story in De Volkskrant, the Dutch newspaper she works for, she began making plans for a trip to the American south. "I wanted to go and search for these families who bought guns as presents for their young children," she says. "I began by visiting a rifle range in Ohio, where children are taught to shoot, then travelled down through Kentucky, Tennessee, Alabama, Texas and Louisiana. What I found was that there are loads of children out there in America with their own guns, but not that many parents who are happy to have their kids' portraits taken with those guns."

Kesteleyn's series, My Little Rifle, consists of only 15 portraits, but they provide a powerful and disturbing glimpse of a much bigger gun culture. Last year, the series was chosen for the World Press Photo's prestigious Joop Swart Masterclass.

Hayley, aged 6, from Louisiana

"I went to gun shops and shooting ranges just talking to people," Kesteleyn explains. "What I came away with was the sense that there was a lot of fear and paranoia among the adults, and that fear was handed down to the children along with the guns. The children have childlike imaginations and the usual childhood fears – zombies, monsters and wild beasts. They are not born with these adult fears; they are infected with them."

Kesteleyn photographed the children in their bedrooms, amid dolls' houses and soft toys. Most of them hold the guns casually, but some strike a tough-looking adult pose. Alongside the portraits, Kesteleyn has included drawings the children made of the things they most feared: spidery outlines of werewolves and wild animals. "My biggest fear is a bear," wrote Benjamin, aged seven, "because if you get in their territory, they will chase you for a long time." Eight-year-old Abby wrote: "What I am freaked out by is seeing a dinosaur."

Tatum, aged 6, from Louisiana

On her journey, Kesteleyn encountered "mostly ordinary families who loved their kids and trained them to use the guns safely and responsibly". Nevertheless, she remained bemused and disturbed. "The adults talked about protection all the time. They believe that you have to have guns to protect yourself from the other bad people out there with guns who want to do you harm."

Some encounters have lingered in her head. "I remember this very young girl who was really tired and worn out after her shooting practice, and that just seemed very sad somehow." At another girl's eighth birthday party, which was held at the local shooting range, Kesteleyn even tried out the child's new pink rifle. "They do feel like toys," she says, "and the bullets are really small – but they can kill another child."