Police fire pepper spray at protestors during a demonstration in downtown Washington on Jan. 20 after the inauguration of President Trump. (John Minchillo/AP)

The American Civil Liberties Union added a 10-year-old boy from North Carolina and his mother to a civil suit it filed against D.C. police, alleging the two were injured while they were protesting President Trump's inauguration in downtown Washington. Police later said they converged on the group to quell a violent riot that erupted.

In the lawsuit, which was amended late Tuesday, the ACLU alleges that the woman and her son were "peacefully demonstrating" at the Jan. 20 inauguration at 12th and L streets NW when police began spraying demonstrators with pepper spray as rioting broke out. The lawsuit says the police knocked the boy to the ground and his mother was unable to remove him from the melee as she was overcome by the pepper spray. Another protester intervened and escorted the woman and her son away from the group.

The original lawsuit was filed in June in federal court on behalf of four plaintiffs, an independent journalist, a legal observer and two protesters. No monetary amount was specified.

The amended lawsuit also identified 27 police officers, including eight supervisors who the suit alleges unlawfully ordered and participated in the arrests of protesters who were not participating in the riots.

The lawsuit quotes D.C. police Cmdr. Keith DeVille, who testified during a trial last month of six of the protesters in D.C. Superior Court. DeVille testified that at the time the rioting erupted, he and other officers were unable to distinguish the rioters from the protesters because the majority of participants wore black and had their faces covered, which prosecutors later said was part of the rioters' plan, when he ordered the mass arrests of more than 200 individuals. The woman and her son encountered police at around 1:45 p.m., about three hours after authorities said the rioting occurred.

Last month, a jury found the six defendants not guilty of rioting and other acts associated with the Inauguration Day violence. An additional 166 defendants are scheduled for trial, in groups of six or seven, through 2018.