Harrah's Casino in California is one of few places that can hold these junior mixed martial arts (MMA) events, because it is situated on an Indian reservation and not subject to Californian Law.
Sunday Night went along to one of these events to see the "junior fight club" that is enraging some and exciting others.
David Bramlette, whose son Mason "The Beast" has been fighting since he was diagnosed with ADHD, says he believes it is safer than most other sports.
"We were driving home and saw a gym on the side of the freeway that said 'kids wrestling', you know, let’s put him in that," Bramlette told Sunday Night reporter Denham Hitchcock.
"I just don’t feel football is safe for a kid, I just I don’t."
Contests are sanctioned and officiated by the US Fight League and follow the limited contact rules which prohibit kicking and punching above the collarbone. Strangling is allowed.
Opponents are not determined by gender but weight range, which means boys can fight girls.
Kids MMA has thrived off the Ultimate Fighting Champion (UFC) craze which has become a $3 billion dollar business.
UFC boss Dana White bought the business in 2001 for just $2 million and says fighting is something humans will never stop enjoying.
"It’s in our DNA. You put two babies on the floor, right. You’ll see this all the time. One baby will take the other babie's thing, the baby smacks the other baby, the baby wants his thing back," White told Sunday Night.
But Daily Telegraph sports reporter Phil Rothfield disagrees.
"Any parent that allows their kids into a cage to kick, elbow, knee, stomp, is not fit to be a parent."
"What parent would let their six or eight year old in the ring to do that? Disgusting."
Bramlette told Sunday Night he chooses to ignore critics.
"(They say) I am a horrible father… how can you do that to your kid?"
Some of these kids do aspire to fight for the coveted UFC title and women's champion Ronda Rousey told Denham Hitchcock just how brutal the competition can be.
"I was willing to kill them and I was willing to die in order to win."
Watch the full interview above.