
But do the parents of the kids at Gillett's think the sport will teach kids to settle disputes with fists instead of words?
"No, my kids have never left here and used it outside of this gym," one parent said. "Never."
In fact, parents often get in the ring themselves, and some said that it's a good way to interact with their kids and that it gets aggressive impulses out in a safe and fun way. There are rules against things like punching in the neck and twisting fingers.
"He likes it as a sport and he likes it to teach him right from wrong," said Mindy Poirier, of her son's MMA experience.
Kim Velozo's 13 -year-old daughter Nicole fights, and Velozo said it's about self-defense.
"If somebody jumps her or something like that, she'll know how to defend herself against whatever," she said. "She loves it. She loves it."
Many of the moms said the training even helped their kids outside the gym, with discipline and following directions.
All the moms "20/20" talked to said mixed martial arts has been good for their kids. Correia doesn't think those parents know how unsafe it is.
"I've heard from doctors who are very concerned about this going on," he said.
"I think it's dangerous from a physical standpoint," pediatrician Lisa Thornton recently told "Good Morning America." "It can lead to significant injuries to the neck and bones and ligaments."
"Mixed martial arts is coining the phrase which means, anything goes," Correia said. "They don't have any rules that are set up by any governing body."
Actually they do have a governing body, the North American Grappling Association, but so what? Hockey has a governing body, but that doesn't stop the fights, even in peewee hockey. No sport is free from injury.
In six years, 77 kids died when they were hit in the chest with a baseball. Many more died riding bikes. No one has yet gathered comparative statistics on the risk of mixed martial arts, but even cheerleading sends thousands of kids to hospitals every year.
MMA participants wear head gear and big gloves to stay protected, and the sport's governing body says it has banned the moves that are most likely to lead to injuries in children. A study from Johns Hopkins found that in MMA there are no more injuries than in boxing.
The kids at Gillett's Gym say they never worry about getting hurt. "We're not in there to hurt each other," said 8-year-old Justin Pereira. "We're all friends here. All the kids are friends and we're just in there to like, go have fun and just learn."