Coroner Shortland made no judgement of responsibility in the crash but rather noted it was "a matter for police whether a person should be prosecuted".
He ruled that Ms Batters was "more than likely distracted for a moment immediately before entering the area where the crash scene took place", either by taking her eyes off the road, being disrupted by the sun's rays or from something coloured ice blue that caught her attention.
Ms Batters had picked her son up from daycare, bought sweets and was heading to her mother's home when she crashed about 4.48pm.
Minutes earlier, motorist Jennifer Waldron crashed into a ditch on the side of State Highway 10 when she was distracted by the sun and swerved to avoid what she thought was a car.
She climbed out of her vehicle and waved for help from the side of the road.
Marcus Boyed, who was driving with his young daughter and son in his ute, pulled over on the highway and began speaking with Ms Waldron through the passenger-side window.
Mr Boyed's car was "partly on the shoulder of the road and [partly] on the highway" but as far to the left as he could manage.
He said he was about to get out of his car when it was hit from behind by Ms Batters.
Ms Batters had possibly been momentarily distracted and noticed Mr Boyed's car too late.
She swerved to avoid it but clipped the back corner and was propelled into oncoming traffic.
In his finding, Coroner Shortland said the crash between Ms Batters' car and the tourist bus was "significant".
"The car, whilst in rotation, has ended up with the front of the car being wedged under the side of the bus before being spat out backwards," he said.
"The impact ... had centred around the seating area where Harlan was strapped into a child restraint.
"The rear driver's side door had been ripped from the car along with significant damage to the ... pillars of the vehicle."
Christopher Dawe, an orthopaedic surgeon from Tauranga Hospital who was on the bus, rushed to Ms Batters' car and to Harlan in his seat.
"His immediate thoughts were that Harlan was critically injured and [he] desperately tried to free him by unstrapping his safety harness," Coroner Shortland said.
Harlan was flown by helicopter to the Whangaroa Health Centre where he was pronounced dead on arrival.
Senior Constable Jim Hawthorn investigated the crash scene, including whether Ms Batters may have been affected by the setting sun as Ms Waldron had been.
Ms Batters said she could not remember being impaired by the sun but it was not ruled out by Coroner Shortland as a possibility.
Coroner Shortland said Ms Batters may also have been distracted by a conversation with Harlan about whether they had seen his grandmother's car in a nearby car park or an item "coloured ice blue" that she recalled may have caught her attention.
Ms Batters' mother, Brenda Batter, said the family did not want to comment.
"It's just been a very hard time," she said.
---
The crash
* 4.30pm - Kelly Batters collects son Harlan Batters-Ellis, 3, from daycare
* 4.30-4.45pm - Ms Batters buys lollies, ice cream, fish and chips before heading home
* Jennifer Waldron, impaired by the sun, crashes her car into a ditch on State Highway 10 near Kaeo
* Marcus Boyed pulls over in his ute to assist Ms Waldron
* 4.48pm - Ms Batters, possibly distracted, tries to avoid the ute but clips it and is sent into oncoming traffic
* Walter Collins, driving the tourist bus, had already slowed but could not avoid Ms Batters' car
* Christopher Dawe, an orthopaedic surgeon on the bus, rushes to help and find Harlan in his car seat
* Harlan is flown to hospital but announced dead on arrival.
