Missouri's attorney general is launching his own investigation of a St. Louis day care center where two workers were accused of facilitating a "fight club" among small children, his office said Wednesday.

The announcement came two weeks after St. Louis prosecutors dropped criminal charges against the former Adventure Learning Center workers.

Attorney General Eric Schmitt's office says it served the day care with a "civil investigative demand" Tuesday to get the center to turn over documents.

"Children are some of the most vulnerable members of our society, and any attempts to harm them in any way will not be tolerated," Schmitt, a Republican, said in a statement.

He did not elaborate on what prompted him to pursue the investigation, and his office did not immediately respond to an email seeking additional information. But Schmitt's office told the St. Louis Post-Dispatch that it's a civil investigation looking into possible violations of the state's consumer-protection law.

The day care's attorney did not immediately respond to a message seeking comment.

Tena Dailey and Mickala Guliford were charged in November with endangering the welfare of a child after video surfaced from December 2016 showing small boys punching each other while wearing oversized, green Incredible Hulk fists. The video shows the two workers watching, with one jumping up and down in apparent excitement. The only person shown trying to break up a fight is another preschooler.

Video of the fight was captured by a surveillance camera and by the cellphone of the 10-year-old brother of one of the fight participants. The 10-year-old, who was in an adjoining room from where the fight occurred, sent the video to his mother, who contacted the center director.

Charges were not filed immediately. But after KTVI-TV aired the video footage in October, Democratic St. Louis Circuit Attorney Kim Gardner reopened the investigation and filed charges. The case was sent to a St. Louis city grand jury, but charges were dropped this month due to "insufficient evidence," Gardner's office said.

Among other things, the charges alleged that a 4-year-old boy suffered a black eye and that the injury came on his birthday.

Both teachers were fired, and the mothers of two of the children have filed a lawsuit.