A video of two children fighting inside a cage has shocked lots of people.
The film shows two boys taking part in a fight, watched by hundreds of grown-ups, in Preston.
The boys were not wearing padding or headgear.
Lots of people think this type of of fighting is dangerous and shouldn't be allowed. But organisers say the boys weren't in danger.
In the video nine-year-old Kian is wrestling an eight-year-old boy.
Kian says he wants to fight and his parents say they're happy for him to do it. His Dad said, "He likes to do it, he's never forced to do it, he wants to do it, so leave him to do it."
Fighting like this isn't illegal. But there are still worries over whether kids should be taking part.
Childrens' charity, the NSPCC, have warned parents against letting their kids do something like this.
The British Medical Association, which represents doctors, said there are other, safer sports that can teach children discipline and help them keep fit.
Kian plans to fight again, and the organisers have said there are more events planned.