Nicholas Keener, 11, and his brother, Calvin Keener, 4, were both killed in a go-kart accident near their home Feb. 18 near Altamont, Tenn. Contributed Photo

ALTAMONT, Tenn. - Slowly, methodically, Wesley and Wanda Keener unload dozens of roses and large basins of plants from the funeral home out of their minivan.

Their eyes bloodshot, dark circles underneath, the couple carry the vases to their tiny living room.

As they cross the room, they pass an open door to the left. Inside, stuffed animals lie piled on a bunk bed. This is the bedroom their three sons used to share.

Now there is only one.

Five days earlier, on Feb. 18, the couple had been watching their boys taking turns riding a go-kart, laughing and spinning around the yard over and over again.

Then came a decision that would end in tragedy: The Keeners allowed 4-year-old Calvin to climb behind the wheel.

After watching his 10- and 11-year-old brothers drive, Calvin wanted to learn. The Keeners decided that was OK. After all, the go-kart had padding on the headrests and seat belts and a roll cage up top.

He was barely able to reach the pedals, so 11-year-old Nicholas operated the gas pedal from the passenger's seat.

Around the yard they went.

Calvin and Nicholas were circling the pine trees and house when Calvin drove down a hill, headed for the road. That's when the Keeners spotted the Oldsmobile heading their way.

Both parents say they ran after the boys screaming, "Cut it! Cut it!" but the go-kart rolled onto the two-lane county road. The driver of the Oldsmobile never even saw them.

The impact flung the go-kart 100 feet.

Calvin was killed instantly; Nicholas died on the way to the hospital.

Their deaths shocked the community and traumatized two families, but doctors and experts say they know all too well the effects of youngsters taking the wheel of an off-road vehicle before they're even able to properly ride a bike.

"Children under 16 don't have the judgment and maturity to manage larger vehicle engines," said Dr. Michael Carr, medical director for the trauma center at Children's Hospital at Erlanger.

Between 24 and 28 children are admitted to the children's hospital for injuries from ATV or go-kart crashes each year, hospital records show.

Nationally, an average of 10,500 injuries from go-kart accidents were recorded annually from 1985 through 1996, according to the most comprehensive study of the issue conducted by the Consumer Product Safety Commission. About two-thirds of the injuries - which included concussions, fractures, internal injuries or burns - involved children under age 15.

A total of 231 go-kart-related deaths was reported in the same period; 155 of them were children.

Common accidents include driving under a house, slamming into a tree or parked car, or flipping the vehicle and being thrown or crushed, Carr said.

But off-road riders and manufacturers say those children are the exception, that the machines are safe. More people wear helmets for recreation, and ATVs with smaller engines are available, they say. Some go-kart seats are adjustable, and the newer models have roll cages.

"Go-karts are safer today then they've ever been," said Reggie Lybrand, owner of Go-Kart World in Newnan, Ga., one of the few go-kart manufacturers in the United States.

Riding go-karts and ATVs on private property and on rough terrain is a common activity, especially in rural communities.

Acres of open fields make it easy to ride close to home and not have to travel to some of the go-kart tracks across the state, some local residents say. And they say it's common to allow kids to start driving at 6.

No laws in Tennessee or Georgia regulate the age children can drive off-road vehicles on private property.

At Lybrand's go-kart shop south of Atlanta, he gets requests for smaller-engine vehicles for kids as young as 3. He recommends go-karts that go only 8 mph and are equipped with modern safety features, such as seat belts and roll cages.

Early on, go-karts - which were invented in the 1950s - were a problem, Lybrand said. The engines were exposed and children could get their hair caught in the moving parts, he said, and they were easily wrecked because the brakes were hard to use. Over the years, those problems have been fixed, he said.

But even he refuses to sell ATVs, saying he stopped selling them eight years ago when he started to hear more about serious injuries and deaths involving children.

"I couldn't sleep at night," he said.

Yet advocates insist that, properly operated, ATVs are safe.

"With an off-roader, safety is first," said Steven Melton, a Tracy City, Tenn., ATV rider and president of an off-highway vehicle advocacy group.

Still, there are more deaths and accidents involving ATVs than go-karts, figures show. In 2009, the Consumer Product Safety Commission reported 649 deaths from ATV-related accidents. Fourteen percent of the deaths were children younger than 16.

In Tennessee, 19 youths age 18 or younger were killed in accidents involving ATVs between 2006 and 2011, Tennessee Highway Patrol figures show. No go-kart-related deaths were reported in that time.

Yet in the past seven months, at least four people have died in go-kart-related accidents from Maine to California, media reports show. One victim was 59 years old, but the others were children - an 11-year-old girl, 9-year-old boy and a 6-year-old boy. The girl, a Mississippi resident, was killed on New Year's Day in Athens, Ala., when the go-kart she was driving rounded a curve in the road and struck a parked car, The Huntsville Times reported.

Safety advocates and doctors say these numbers are unacceptable and that parents are partially to blame.

"The real tragedy is when a child is airlifted with an emergency ... and the parents say, 'We'll get you another one,'" Carr said.

Off-road vehicle accidents are often caused by speed, riding too close to vehicles and other equipment or the driver not having the strength and coordination to operate the machine, said McMinn County Sheriff Joe Guy.

"You're literally unrestrained, sitting on top of a motor," Guy said.

ATV wrecks are more common, he said, and that could be because go-karts are closer to the ground and have the protective roll bar.

Another factor to consider is that go-karts more commonly are used on racing tracks and ATVs on rough terrain, said Clay Carlock, safety coordinator for Erlanger's Safe and Sound program. In a controlled environment like a track, accidents are less frequent.

The right age for children to operate off-road vehicles depends on their weight, size and maturity level, Carlock said. The smallest ATV engines, under 70 cc, are recommended for children ages 6 to 12, but 90 cc engines and larger shouldn't be operated by anyone under 16, he said.

But some safety advocacy groups don't recommend anyone under 16 driving an ATV.

In the deaths of Calvin and Nicholas Keener, Tennessee Highway Patrol officials say no one has been charged. District Attorney Mike Taylor, of the 12th Judicial District, declined to comment on the potential for charges, saying he hasn't seen the final report.

The go-kart Calvin was driving had a lap seat belt, but THP spokeswoman Dalya Qualls said it was unclear whether the boys were using it because both were thrown from the vehicle. Neither boy was wearing a helmet, she said.

But Wesley and Wanda Keener said the boys were always told to wear their seat belt. The couple would watch the boys outside when they rode the go-kart and had a strict rule not to drive in the road.

The couple always thought they were taking the necessary safety precautions.

"It all happened too fast," Wanda Keener said. "There was nothing we could have done."