The teenager, who cannot be named, pleaded guilty to the five charges at Leeds Crown Court after the crash in November.
Ellis Thornton-Kimmitt, 12, his brother, Elliott Thornton-Kimmitt, 14, Darnell Harte, 15, Robbie Meerun, 24, and Anthony Armour, also 24, all died after the crash involving a Renault Clio in Stonegate Road in Leeds.
At a previous hearing, the boy had wept in the dock as the details of the accident in the Meanwood area of the city were given to the court.
Appearing in court by video-link on Wednesday, the boy was told that reports would be prepared and he would be sentenced on January 26.
The car involved in the crash had been stolen in the Headingley area of Leeds at 6.30pm the same evening before it crashed into a tree shortly before 10pm.
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The 15-year-old was taken to hospital with serious but not life-threatening injuries after the crash.
Detective Chief Inspector Jim Griffiths described the scene that met emergency services as “total carnage”.
One man who lives close to the crash site said after the incident: “It was unbelievable. You couldn’t even recognise it as a car. It was just a crumpled mess.”
His wife added: “There were bodies laid about, it was awful. It was as bad as that. We were just sat here and we just heard an almighty crash.”