Jan. 21, 2014 -- It's 7 o'clock on a school night in Prachinburi, a village outside of Bangkok, Thailand, and hundreds have gathered in a boxing arena to watch children beat the living daylights out of each other.
Many boys and girls, between the ages of 7 and 9, participate in a form of boxing known as Muay Thai. These kids compete for money, often through widespread gambling -- bets placed on who will win.
During their fights, which occur almost every night of the week, these kids don't use head gear, mouth guards or any other form of protection. All they wear are shorts and a pair of boxing gloves. Even at this young age, many have been training for years.
This isn't some secret backroom sport, but a national pastime in Thailand, fully engrained in Thai culture, mainly in poor communities. But this form of fighting can have dangerous consequences. Videos of these fights have captured some disturbing moments, including a child vomiting in the ring, crying and wanting to quit, only to be sent back in. In another video, a little girl's eyes can be seen rolling back into her head. Doctors say she suffered a seizure from the blows she took.
In this surreal scene of pint-sized boxers, ABC News met a stone-faced 7-year-old named Andy, who was preparing for his first fight.
When asked if she was worried about her son getting hurt, Andy's mother said through a translator that "I'm not scared ... because I want to teach him to be tough."
Andy said he liked to fight, "because I get money," but his first match didn't last long. The refs called it off early, fearing the little boy was outmatched by his opponent.
A 9-year-old girl named Poomrin is typical of many of the young fighters. After school she heads to a makeshift boxing ring built atop of a crumbling old dock along a river. She has 15 brothers and sisters -- and all of them fight. Poomrin and her 15-year-old sister Pavida said they have had their lips cut and teeth broken in the ring.
Poomrin said she had been in 11 fights and won all of them. Her sister said she has fought 41 and lost half of them.
Their training is endless. Fighters jog every day, exercising and drilling repeatedly. Even the smallest children are expected to join in. The girls' father, a former fighter himself, said he had no concerns about his children's safety in the ring. Their proud mother showed off the family's overflowing stash of trophies and prizes.
"It's a sport and there are bigger problems," Poomrin's mother said through a translator, adding that it keeps the kids happy, focused and away from drugs.
Many families believe fighting keeps kids away from other dangers, and in this culture, there are few alternatives for success. Some of these kids would be working in sweatshops or put to work in Bangkok's infamous red light district if they weren't in the ring.
Filmmaker Todd Kellstein spent years inside Thailand's child boxing culture for his film, "Buffalo Girls," which follows the lives of two young girls whose families rely on them to win in the ring and bring home money. Kellstein said watching families place bets and encourage their children to fight in the ring was difficult for him to watch at first.
"It's something I struggled with quite a bit during shooting and editing. I went there with a very Western perspective," he said. "But it was only after three years of coming to grips with Thai culture, to realize that it is a way of life and none of our business to judge. ... These kids are putting their brothers and sisters through school ... paying for [their] parents' house, paying electric bills."
Some American kids have taken up a version of cage fighting, but with protection and a lot more parental concern. Yet in Thailand, researchers estimate 100,000 kids under age 16 actively participate in Muay Thai, and doctors are worried that these little boxers are doing serious damage to their brains.
Dr. Jiraporn Laothamatas is part of a team in Bangkok working on the first-ever research into how this fighting is affecting children by conducting brain scans and other tests on 100 child boxers. She said early tests are far worse than she imagined when she began the project, and that the scans of these children's brains look like those of people who have been in a car accident.
One of the kids being tested is 10-year-old Thipsajja. Like others, she too came from a fighting family and is poor. Thipsajja shares a tiny apartment with her brothers and sisters and hopes that her fighting skills will be her ticket to a better life. Her father set up a makeshift boxing ring next to the police station where he works so she can train.
She is shy, but focused and fearless in the ring. Her mother, speaking through a translator, said that at first she was very scared her daughter would get hurt, "but after seeing her in practice and the fact that she learned how to protect herself, she feels a little better" about Thipsajja fighting.
Data collected on these kids show that child boxers, due to their intense training, have better hand-eye coordination than other kids, but they also have serious memory issues that researchers say will grow worse. Laothamatas' biggest concern was evidence of iron build-up in the brain, which she said shows bleeding in the brain.
Laothamatas said she faces an impossibly steep uphill battle and her work at the hospital is not popular. She said she had one fighting coach come in and demand to know why she was doing this research.
"When we tried to explain, he didn't want to listen," she said.
Disturbing as the early research is, it may not make a difference in a culture not yet ready to hear it and unprepared to offer a better way out.