Both boys shot at Danny Andrew Smith with a rifle as he rode his tractor in the field near Westminster on June 23, Oconee County Sheriff Mike Crenshaw said in a statement.
Smith, 62, was shot once in the back, but investigators charged both boys because they both fired the gun in Smith's direction, Crenshaw said.
"After a consultation with the Solicitor's Office, and based on the evidence obtained in our ongoing investigation, we believe that both juvenile males discharged a firearm in a reckless manner in the direction of Mr. Smith who was bush hogging on some family property," the sheriff said. "At this time, it is still undetermined which shot ultimately struck and killed Mr. Smith. However, based upon South Carolina law, the hand of one is the hand of all and that is why Family Court has been petitioned in regards to charging both juveniles with Involuntary Manslaughter."
Under South Carolina law, they are too young to be kept at a juvenile jail so they were released to their parents, the sheriff said.
Deputies have the .22 caliber rifle used to kill Smith.
"The Sheriff's Office is continuing its investigation and due to that fact, no information will be released that will identify the juveniles in this case," the Sheriff's Office said. "At this time, no information about motive or where the firearm was obtained will be released due to the ongoing investigation and any additional details will be released as conditions and developments warrant."
Smith's wife found him slumped over in the driver's seat of his tractor, which was still idling after it ran into the woods and struck a tree. An autopsy found he had been shot in the back about four to six hours before his body was found.
ABC News and the Associated Press contributed to this report.