The expert phase of Coroner Alexander Ho’s inquest into the 3-year-old’s death continued in Invercargill today.
In 2019, Lachie was found 1.2km from his Gore home, face up in an oxidation pond.
Lachie’s father Paul Jones never believed his son drowned and suspected foul play.
Today Megan Fowler, a clinical psychologist and paediatric neuropsychologist, said Lachie running 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."
The witness said the running away 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 kids Lachie’s age were "really quick" and generally loved to play in water.
"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.
She explained that young children lack consequential thinking which can lead them into potentially dangerous situations.
Because of his limited experiences, Lachie would have found it difficult to find his way back home if he had found himself to be lost, Ms Fowler explained.
The inquest will continue tomorrow.
