Pledger could not understand how Declan and his two older brothers had accessed the pool.
"All the gates were shut. The father shut the gate and the children were behind a ranchslider.
"The only way they could get out was through the back of the garage and we were checking that. For some unknown reason they got through the gates," he said.
"Somehow they got out and the little boy - he's just started walking - he followed his big brothers. They were curious about the fire. He lost his footing and stumbled down a bank into the ashes."
Declan's father saw him and ran to pull him out.
The infant was treated by St John Ambulance staff before being flown to Auckland's Middlemore Hospital.
He underwent surgery on Friday at the hospital's specialist burns unit.
"He burned his hands and feet and may have to lose his fingertips," Pledger said. "He's expected to make a full recovery but may have lasting issues and scars, but we'll see.
"It is looking good for him. Middlemore is the best in the country for burns."
Declan was still in the intensive care unit yesterday.