Martin Cawley, 19, was sentenced to two years in prison at Wood Green Crown Court for kidnap, child abduction and aggravated vehicle taking.
The reckless teenager was high on drugs when he took the parked car and drove off in north London on July 2.
A court heard the little girl managed to escape by jumping out of the Vauxhall Astra — grazing her arm — shortly after Cawley drove off, despite her shouting “no, no”.
The 11-month-old baby boy was later found, uninjured, on the doorstep of a house in Cheshunt, Herts.
Dramatic footage issued by cops as they hunted for Cawley in the summer showed the girl leaping from the back of the car.
The court heard Cawley, who had no driving licence, abandoned the baby outside a block of flats after a three-miles journey at high speeds.
Callous Cawley, of Kentish Town, north London, then headed to his nearby aunt”s house to smoke a joint.
Nick Cribb, prosecuting, said: “At the plea hearing the Crown said this represented every parents worst nightmare, and it is a position we do not renege on.
“This was an offence of unspeakable cruelty to the children and their parents.
“When high on drugs, Mr Cawley stole the family car with their two children.”
Tom Kharran, defending, said Cawley”s mum had been a drug addict since he was a child.
Cawley admitted the charges.