http://cnnphotos.blogs.cnn.com/2013/10/25/kids-mma-2/ wrote:Thunderdome for children

The combatants: Two mixed martial arts fighters. Their field of competition: a cage.

With their hands and feet, they punch, kick, tackle and choke each other. And then, sometimes, they cry.

Welcome to Thunderdome,  where winners and losers can be as young as age 5.

It's called kids' MMA, or Mixed Martial Arts, and New York-based photographer Sebastian Montalvo pulls back the curtain on one of the nation's fastest growing youth sports, which claims more than 3 million boys and girls.

Some call kids' MMA a disturbing new facet of American culture tainted with safety and behavior issues, but supporters tout it as a tool that encourages discipline, exercise and self-confidence. Little League Baseball, this ain't.

Montalvo's images of young children engaged in intense full-contact fighting can be disturbing to those who've never seen the sport before. Protective equipment often doesn't include headgear, only gloves that are thinner than boxing gloves. The photos depict the sport's intense physical spirit, where referees oversee children who score points by pummeling each other.

At a match in Sacramento, California, Montalvo captured Kristopher Arrey's war face. His reputation has earned Kristopher the nickname, "The Arm Collector." He's 7.

Montalvo's photograph shows Arrey on his back, grimacing, nostrils flared, crushing another boy in a chokehold. The other boy - Mason Bramlette - also age 7 - is seen in another image, crying. The judge has stopped the fighting, while Mason holds a gloved hand to his face after getting the wind knocked out of him.

"Are you OK?" Montalvo recalls the referee asking Mason. "Do you want to keep fighting?" Mason's father urges his son to stay in the cage.

What struck Montalvo the most about the kids' MMA culture, he said, was the importance of winning among the parents. "They're mega-competitive," Montalvo said. They "love their kids 100%" and "they just want them to win."

Parents also see MMA as a gateway to teaching kids other concepts besides victory, such as courage, defense against bullies and good sportsmanship.

"After every match, the kids are supposed to shake hands," said Montalvo. "One father started screaming at his son because he didn't want to shake hands after he lost.”

The father told his boy, "'You go and suck it up and do it!'" Montalvo recalled. The young fighters then shook hands.

Kids MMA has been fueled by the massive success of professional mixed martial arts, led by the Ultimate Fighting Championship, or UFC. This youngest generation, Montalvo said, is growing up under UFC's global fame and popularity, a powerful cultural influence.

Young fans see MMA pros like Tito Ortiz, B.J. Penn and Chuck Liddell on TV and online. They look up to these athletes and spend millions buying the sport's memorabilia. "A lot of these MMA parents want their kids to go pro someday," Montalvo said. "They want them to earn million-dollar paychecks."

–Thom Patterson, CNN