A day care center in St. Louis encouraged toddlers to viciously brawl with each other in a "fight club," according to a lawsuit from the mother of one of the children and video of the incident that was released Wednesday.

Nicole Merseal said her then-4-year-old son, and another child were instructed by teachers Mikayla Guliford and Tena Dailey, to punch and hit each other at the Adventure Learning Center in December, 2016, according to the suit filed earlier this year.

Merseal, of St. Charles, Missouri, accused the day care in court documents of permitting another child "to intimidate and harm" her son while directing a "fight club."

The video shows Merseal’s youngest son and another boy wearing Incredible Hulk toy fists and punching each other while a teacher looks on.

One of Merseal's sons recorded the episode on his iPad and sent it to her. She then called the police and had them visit the day care and interview the director and staff. Her children were also questioned by investigators.

In documents released by the Missouri Department of Health and Senior Services, Jennifer Scott, the director of the center, said that when she confronted Guliford about the incident, she said the children "were bored" and that "we ran out of things to do."

Scott fired Guliford and Dailey and contacted the Child Abuse and Neglect Hotline, according to the health department.

Guliford admitted to having the children fight, according to state documents. She said she took the children to the lower floor of the building because of a broken heating system on the other floors.

"I meant for the fighting with the Hulk Hands to be a stress release exercise," she said. "It did not last more than three or four minutes."

Guliford said no children were hurt in the incident but "it was still a bad judgment call on my part."

But the St. Louis Circuit Attorney’s Office declined to prosecute the teachers.

"There was insufficient evidence to prove beyond a reasonable doubt that any laws were violated,” the agency said in a statement to NBC News on Wednesday. "However, that does not diminish the incredibly poor judgment by these adults who had the responsibility to safely supervise these children. If anyone has information about this matter, we encourage they contact our office."

The city's Department of Health and Senior Services conducted an investigation upon learning of the incident and concluded the facility reported it to the proper authorities.

"The Section for Child Care Regulation’s report concluded that licensing rules were violated and requested that the facility take additional steps to ensure staff were trained and knowledgeable about age-appropriate activities for children,” the St. Louis Department of Health and Senior Services said in its report. “The facility completed the corrective measures in April 2017."

Merseal filed her lawsuit because she believes those actions were not enough.

"The punishment wasn't enough," her lawyer, Jennifer Hansen, told NBC News.

They are suing the day care for negligence, recklessness and breach of contract and seeking $25,000 in damages.