Kamala Bai (61), grandmother of the schoolchildren who were murdered recently, identified the accused in an identification parade held at the Coimbatore Central Prison in the presence of Judicial Magistrate Deivam.
She identified the accused from among several others who were lined up along with the accused.
Kamala Bai is said to have seen the children board the vehicle.
There were as many as three rounds in the identification parade, which was conducted in the prison in the presence of the magistrate.
Police have arrested two persons, Mohan alias Mohanakrishnan, a former school vehicle driver known to the children and an accomplice Manoharan of Angalakurichi.
The ten-year-old girl and her seven-year-old brother were abducted from RG Street in the city on October 29.
While the girl's body was found the same day, the boy's body was recovered on Sunday.
The accused have been remanded to judicial custody and have been lodged in the Coimbatore Central Prison.