Mr Going was unsure if the boy was wearing a helmet.
Mr Hodson said although the beach was legally a highway with a 100km/h speed limit, it was very different surface from the road.
"You've got to respect the terrain you're travelling across. The sand can move and it appears it was very light sand the boy hit. That's the nature of the beach - it's always changing. You can travel across it one day, and the next day encounter big holes."
The death brings the region's road toll to two, after Whangarei motorcyclist Karlton Hughes collided with a car travelling north on Murrays Rd, 5km north of Tangowahine Valley Rd on January 5.
The beach tragedy comes a week after 11-year-old Whangarei boy Jahzel Porter drowned after getting caught in a rip at the mouth of the Waipu River - the third drowning in the region in 12 days.
Auckland student Heng Li, 25, drowned while setting crab pots on Uretiti Beach on Christmas Day and Jarod Lineses, 16, was swept out to sea at Ninety Mile Beach on December 27. His body was found on New Year's Day.
Meanwhile, on Saturday the search was scaled back for a 25-year-old male diver who went missing near Cable Bay last Thursday.
The head of Northland Police Search and Rescue Senior Sergeant Cliff Metcalfe said the man was presumed dead, and the search had been scaled back to local police staff patrolling the beach. Police have not released the man's name.
The man had been free-diving with a friend at the eastern end of Cable Bay, and when after three hours his catch-bag and a glove washed up on the shore, police and emergency services began the search.
The police dive team worked between 11am and 8pm last Friday but found nothing.
Saturday's go-kart crash was one of a host of beach accidents in the Far North in the past few weeks.
A woman badly broke her arm after a buggy accident on Ninety Mile Beach on December 29. The day before, a teenage boy suffered back injuries in a quad bike crash at a coastal campsite near Mitimiti, North Hokianga and another woman hurt herself while dune boarding at Te Paki dunes.
On Christmas Eve, a man is believed to have misjudged a jump on a sports quad in dunes near Tauroa Pt, suffering back injuries.