A mother whose 4-year-old son was killed in front of her by an out-of-control teenage motorist says the driver is not a bad person and she does not want him jailed.

Emma Woods was relieved yesterday when Ashley David Austin, 18, admitted dangerous driving causing the death of her son Nayan, and injury to herself and her other son Jacob, 6, as they were walking on a footpath in suburban Christchurch on May 21.

"We're glad that we don't have to go to trial and relive anything or be a witness or anything like that," Mrs Woods said.

Austin's guilty pleas in the Christchurch District Court mean he could face up to five years' imprisonment on each of the three dangerous driving charges.

He also admitted driving a modified car unfit for public roads.

A vehicle inspector found the Nissan Silvia Austin was driving had been modified to the point where it was "only suitable for a controlled environment like a race track".

"I guess he made a mistake that had pretty horrendous consequences, but that doesn't make him a bad person," Mrs Woods said.

"And he's done a lot since the accident to attempt to make amends or try to support us.

"I don't think somebody like him belongs in jail. I don't think he's going to learn anything from being in there. The mistake he made, he's not going to do it again."

Mrs Woods and her family had met Austin and his family, and found them to be "nice people".

Austin, who has no previous criminal convictions, made no comment outside court.

But his mother Brenda said it was a "horribly tragic thing that everyone has been put through - a mistake".

The court heard Austin was driving from work in the Nissan, registered to his mother, when he turned into multi-lane Linwood Avenue, and accelerated in first gear in what witnesses described as a "controlled drift", but which Austin said was not deliberate.

When he changed into second gear while still accelerating, the car swung out at the rear and Austin lost control.

The car mounted the grass verge, drove across the footpath and ran head-on into a small fence.

It then rotated about 180 degrees and struck Mrs Woods and her two sons, coming to coming to rest on top of Jacob.

Nayan suffered the worst injuries, and Mrs Woods, Austin and police and paramedics tried in vain to resuscitate him. Jacob had multiple injuries, including fractures, and Mrs Woods had extensive bruising.

Austin later told police he felt he was too quick with the clutch while changing from first to second gear in high revs, and this was not his "everyday type of driving".

A vehicle inspector's report showed the car had lowered suspension with stronger springs to enable the car to slide easier, and the hand brake did not work on the rear wheels.

The modifications could have contributed to the cause of the crash.

Austin is to be sentenced on October 20.