Legal advocacy groups have filed a lawsuit against a Kentucky sheriff's deputy who handcuffed two children with mental disorders in an elementary school in 2014, alleging that the students suffered trauma after being punished for behavior that they could not control.

Video of one of the incidents shows Kevin Sumner, a deputy with the Kenton County Sheriff's Office, pulling an 8-year-old boy's arms behind his back and placing handcuffs on his biceps. The third-grader — identified in the lawsuit by the initials S.R. — cries out in pain.

"You need to behave the way you know you're supposed to, or you'll suffer the consequences," Sumner tells the boy.

"If you want the handcuffs off, you're going to need to behave as I'm asking you — nicely," Sumner says. Sumner was assigned to work at Covington Independent Public Schools, a school district located in Kentucky just across the Ohio River from Cincinnati. After attempting to discipline the student, school officials reportedly called Sumner to restrain him.

Various legal advocacy groups, including the Children's Law Center and the ACLU, filed the lawsuit against Sumner on behalf of the boy and another child who was restrained. The plaintiffs are seeking a change in policies by the Kenton County Sheriff's Office, and additional training for police officers who work with special needs children.

S.R. had previously been diagnosed with attention deficit hyperactive disorder (ADHD) and post-traumatic stress disorder (PTSD), according to the lawsuit.

Sumner also reportedly restrained a 9-year-old girl — identified as L.G. — earlier in the year in his police cruiser after a teacher asked for her to be escorted to another room. The girl had also been diagnosed with ADHD, and was handcuffed by Sumner in two separate incidents, according to Mother Jones.

"These disciplinary practices… feed into the 'school-to-prison pipeline,' where children are funneled out of public schools and into the criminal justice system," the ACLU said in a statement. "Many of these children have disabilities, yet instead of receiving necessary educational and counseling services, they are often punished and pushed out."

The video is the latest case where police use excessive force on children in public schools has been documented. According to Mother Jones, which has been tracking incidents of police violence against K-12 students, at least 28 students have been seriously injured and one killed by police in the last five years.