Martin Cawley, currently of no fixed address but originally from Kentish Town, pleaded guilty at Wood Green Crown Court to kidnap, child abduction and aggravated taking and driving away.
On the afternoon of July 2, a 27-year-old woman left her two children - a 12-year-old girl and a baby boy - in her car while she went into a shop in Kempe Road, Enfield.
Cawley then got in the car and drove off at speed.
The terrified girl escaped by throwing herself out of the car and into the road, while her 11-month-old baby brother remained in the car strapped in his car seat.
On seeing her car drive away with her baby son and with her daughter lying in the road, the panic-stricken mother immediately called police.
The baby was later found unhurt on the doorstep of a house in Cheshunt in Hertfordshire.
The girl was treated for minor injures, but she did not require hospital treatment.
Cawley was identified as the suspect and arrested on July 19.
The prosecution said he was high on drugs when he stole the car.
He was remanded in custody for sentencing on October 14.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here