A 14-year-old boy has admitted causing a horror Boxing Day car crash that killed three of his friends.

Cole Troy Christensen-Hull, Samuel "Sammy" James Drost and Lily Frances Moore - all 15-year-olds from Canterbury - died when a car they were passengers in failed to take a corner and crashed into trees on Southbridge-Sedgemere Rd, near Leeston, in the early hours of December 26 last year.

The unlicensed 14-year-old driver, who was badly hurt in the crash, pleaded guilty yesterday at the Youth Court in Christchurch to three charges of dangerous driving causing death and one count of dangerous driving causing injury.

Youth advocate Tony Greig said the guilty pleas came after a family group conference.

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Judge Jane McMeeken remanded the teenager for sentencing on June 6.

A social workers report and plan will be prepared ahead of sentencing.

The five teenagers, who were all high school friends, were travelling in a Nissan Tiida after visiting a nearby camp site.

It's understood that the car had been travelling at 111km/h on Harts Rd when it hit a grassy mound, which launched the car across Southbridge-Sedgemere Rd into a macrocarpa hedge.

The only occupant wearing a seatbelt managed to flag down a passing motorist who phoned emergency services.

Just days after the crash, Lily's father Marcus Moore said he had forgiven the 14-year-old driver, and wanted to encourage other youngsters to make good choices in life.

"He's a good kid. He has to live with it for the rest of his life and we have to grieve for the rest of our lives," Moore said.

Nineteen people died on New Zealand roads over the Christmas and New Year period.