Citing the city's civil affairs bureau, the report said most of the children at the club came from the impoverished prefecture of Liangshan, and it was up to the civil affairs authority there to decide whether they should be adopted.
Tong Xiaojun, from the China Youth University of Political Studies, said a company had to meet specific criteria and have the approval of civil affairs authorities to be able to adopt children, the Xiaoxiang Morning Post reported.
The club did not reply to a request for comment.
In the documentary, club founder Enbo, a Tibetan and former armed police officer, said he started the martial arts team in 2001 and encouraged the children to join to stop them turning to crime.
"Some of these kids were orphans, and some had a family that was too poor to educate them," he said in the video.
The children were adopted legally and the adoptions were endorsed by the government, he said.
Enbo said some club alumni went on to become bodyguards or do well in national martial arts competitions.
In the video club coach Dong Zhou said some children said the training was too much for them and they wanted to leave.
"I ask them: 'What can you do if you return to your hometown? Herd cattle or raise pigs? Beg for food on the street, or be a delinquent?"
Xiao Wu said in the documentary that conditions were better at the club and he did not want to return to his former home.
"There is everything here - food, clothes and a place to live," Xiao Wu said. "The food here is much better than at home. There is beef and eggs here, but at home I can only eat potatoes. [If i go back home] I will have to take up labouring jobs."
He said his parents had died and his grandmother sent him to the club three years ago.
Xiao Long said his father was dead and his mother had abandoned the family.
Both boys said their goal was to win the Ultimate Fighting Championship, a Las Vegas-based mixed martial arts competition.
Online opinion on the adoptions was mixed, with some accusing the club off profiting off the backs of children and others saying it was better than having the teens be idle in their hometown.
"The children are clearly aware that they can have a bright future there; but returning to Liangshan, it's definitely impossible for them to live well," one commenter said.
-South China Morning Post
