The man, now 25, was charged last year with a range of offences, including organising a street race, after two boys, aged nine and 10, died when the Subaru WRX they were travelling in left the road and hit a tree in Monterey on August 25, 2023.
Today, police charged him with two further counts of manslaughter over the deadly alleged race.
He will next appear in court on May 2.
Another child – a nine-year-old girl – survived the incident with relatively minor injuries.
Police allege the Subaru was being driven by a second man and was racing an Audi A4 being driven by the now 25-year-old when the crash occurred.
The second man remains in custody after being charged with two counts of aggravated dangerous driving causing death, and one count of causing bodily harm by misconduct.
A 24-year-old woman who was allegedly in the Audi with the now 25-year-old during the crash is on conditional bail after being charged with concealing a serious indictable offence.
She is next due in court on 11 April 2024.
