The Special Investigations Units mandate was invoked after a Wellington OPP officer shot two youths with anti-riot rounds on November 21.
According to the SIU's preliminary information, the boys did not suffer serious injury.
OPP were called to a Harriston residence on Tuesday to investigate a disturbance. According to officers, when they arrived, they found two males causing damage to the residence. An officer shot both with Anti-Riot Weapon Enfield rounds.
They were arrested and taken to local hospital.
The SIU says the mandate was invoked because police officers discharged a less-lethal weapon, which is classified as a firearm.
Anyone with information on the incident is asked to contact the lead investigator at 1-800-787-8529.