An Alice Springs police officer who failed to stop and help a group of children who had been injured in a car crash and told a junior officer not to call for assistance has been sentenced to jail.

Chinthaka Hettirachchi, 42, was a constable on youth patrol with a probationary officer on May 9, 2014, when they followed a car which had "reversed away aggressively".

They lost sight of it on a dirt road but later found it on its side, crashed into a tree.

Inside were five boys aged 10, 11, 12, 13, and 15.

The 12-year-old driver had a fractured foot, the 13-year-old had a broken arm and internal bleeding and required life-saving surgery, and the others were scraped and bruised.

In sentencing Hettirachchi earlier this month, Justice Dean Mildren said the officers twice drove past the crashed car without stopping to help, and Hettirachchi told Probationary Constable Erica Hicks: "you didn't see anything".

Hettirachchi pleaded guilty to attempting to pervert the course of justice, as well as five counts of "being able to provide rescue, resuscitation, medical treatment, first aid or succour of any kind to a person urgently in need of it and whose life may have been in danger if it was not provided, but callously failing to do so".

But when initially questioned by his supervisor, Hettirachchi also denied ever having seen the car.

"You must have realised that the accident was serious and ... the possibility that the occupants were injured," Justice Mildren said.

"You had two opportunities to (stop) but you did not do it and you even went so far as to stop Probationary Constable Hicks from calling in help."

He said Hettirachchi knew he was doing the wrong thing, and attempted to cover up his wrongdoing by lying to his supervisor, but could not infer that the officers knew the car's occupants were children.

Hicks, then 20, left the NT Police Force and Hettirachchi was forced to resign from what Justice Mildren said was his "dream job".

Hettirachchi was previously a person of good character who had expressed remorse and contrition, he said.

But "the public are entitled to expect a lot more from serving police officers", he added, and sentenced Hettirachchi to a total of three years in jail, discounted for an early plea, to be suspended after 12 months served.