Mr Kennett said after playing the curtain raiser, and then watching the first half of the Heartland game, the team returned to the camp and the boys played touch rugby.
Some of the youngsters decided to walk down to the river, but one of them disappeared.
"It wasn't until teatime that we realised we had one missing. Some of the lads thought he may have gone back down to the river.
"Six of the parents, we all scarpered down there. Myself and my assistant coach walked about 100 metres up the river. The others went the other way.
"We searched all round camp, and no sign, so there was only one call to make, and that was to the police.''
Two search and rescue teams, two search dogs and a police dog hunted through the night.
The Solid Energy Rescue Helicopter and pilot with night vision gear were also called in to help the search.
West Coast police search and rescue co-ordinator constable Mike Tinnelly said the boy told them he had heard the helicopter but was unable to attract its attention as the bush was too thick.
"It had been seven or eight hours by then ... he only had his t-shirt and shorts on,'' Mr Kennett said.
"Luckily it was a pretty warm day, but by 2am it started getting really cold. It was then, it started getting really quite serious.''
A search dog eventually found the boy sitting on the creek bank, about 2km from the lodge, at around 5am.
"When the search dog found the boy he was chatty, cold and relieved, but a bit worried that the dog, a german shepherd, was going to bite him,'' Mr Tinnelly said.
He was taken back to the lodge for a feed and a hot shower.
The boy's mother and grandfather had driven over from Christchurch in the middle of the night and were "very happy'' to see him.
Mr Kennett said he was tasked with explaining to her what had happened when she turned up at around 1am - halfway through the search.
"The first thing she saw when she came into the camp was all the police and search and rescue vehicles,'' he said.
"She was pretty good actually, quite calm.''
Mr Kennett said the boy was "still in shock, and a bit shaken up'' today.
His mother did not return APNZ calls.