The expert phase of Coroner Alexander Ho’s inquest into the 3-year-old’s death continued in Invercargill yesterday.
In 2019, Lachie was found 1.2km from his Gore home, face up in an oxidation pond.
Police quickly concluded the boy had drowned, but later said they "missed some steps" in the investigation.
Lachie’s father Paul Jones never believed his son drowned and suspected foul play.
Yesterday, Megan Fowler, a clinical psychologist and paediatric neuropsychologist, said Lachie running 1.2km away from home, in the way his mother described, was plausible.
"Lachie appears to have enjoyed hide and seek, and chasing or being chased by others, and enjoyed running away, as part of his play", she said.
"It is possible that Lachie continued to run, in the hope his mother would chase him, before realising she was not in sight."
Ms Fowler said the fence near the oxidation pond had sufficient hand and foot holds for a child of Lachie’s age to climb it.
"It is possible that a child of Lachie’s age, and physical development, would be able to traverse a certain distance, through the novelty of the experience, excitement of playing a game, fantasy play and/or distractions that draw them onward.
"I think an energetic, physically active child ... would be able to cover a distance like that, although it may not have been the intention to do that, of course", she said.
The witness said the running may have initially been a game for Lachie, but when he realised he was lost and alone that may have changed.
Upon realising he was lost, a spike in stress hormones may have caused Lachie to experience a new level of physicality in an effort to survive, the witness said.
She explained that while Lachie may have been tired after 9pm when he went missing, children were not aware of fatigue the same way as adults and often "keep going until they drop".
She said children Lachie’s age were "really quick" and generally loved to play in water.
Young children lacked consequential thinking which could lead them into potentially dangerous situations.
"Testing boundaries is a normal part of child development", Ms Fowler said.
"A feature of Lachie’s developmental period is a child’s increased physical mastery, their pleasure in this, and their attempts to push the boundaries of what they are capable of, as they learn more about their bodies."
Because of his limited experiences, Lachie would have found it difficult to find his way back home if he had become lost, Ms Fowler said.
While some things were hard to assess without meeting Lachie, and there was a wide range of tendencies in children, she based her opinions on how children Lachie’s age typically behaved.
The initial running away from home to Deborah Thurston’s house made sense because of Lachie’s age and stage.
The inquest continues today.
felicity.dear@odt.co.nz , PIJF court reporter
