Their mother had left the pair, aged five and nine, in the car with the engine running in a neighbour's driveway at Arthur Griffith Park, Lucan.
A man then jumped into the driver's seat of the blue Wicklow registered BMW and drove away with the two distraught children still on the back seat.
Apparently, the car thief was unaware of the children's presence. When he realised what had happened, he pulled over and left them on the side of the road. The children were unharmed and were able to find their way safely back home.
"The man responsible is described as being Irish, going bald and was wearing a blue hoodie with a black jacket," said Sergeant Mark Campbell of Ronanstown Garda Station.
The car has not been found since and gardai at Lucan are investigating the incident. Anyone with information should contact them on 01-6667300.
No one has been arrested in connection with the incident which is the third such hijacking involving children in the space of two months.
Last month, thieves sped off in a car with a seven-month-old baby asleep in the back seat.
The boy was reunited with his distraught parents when the car was found abandoned a short distance away -- with the infant still soundly asleep.
The drama unfolded when the boy's father was dropping off an item at Avondale Park, Mulhuddart, north Dublin.
Two months ago, a 20-year- old man was charged with hijacking a car with a 10-year-old boy inside in Dublin on August 5 last. The boy managed to get out when the car stopped.