The police serious crash unit was investigating the incident.
Police said the name of the child, who did not live at the property where the fatal crash occurred, was not yet available.
"The family has requested that their privacy is respected at this difficult time.''
Federated Farmers health and safety spokeswoman, Jeanette Maxwell, said strict guidelines governed the use of quad bikes on farms.
No child under 16 should be in charge of an adult-sized quad bike, she said.
"When it comes to having a young person on the quad bike, it depends on the circumstances.
"Say there's an emergency, and you need to dash off and deal to something like an animal welfare type-thing ... you may be in a situation where you are forced to take the child with you.''
Sometimes, leaving the child or children home-alone puts them in a more "serious-harm situation''.
"You can't always say it's an absolute no,'' she said.
Many farmers also lived in isolated areas meaning it was impractical to find alternative child-care arrangements at short-notice.
Taking young children on quad bikes was not common practice, Mrs Maxwell said.
Children and quad bikes:
• May 2014: Four-year-old understood to be riding a quad bike with an adult dies in hospital after a crash at a Canterbury farm
• January 2014: Charlie Vercoe, 6, fatally injured while riding an adult-sized quad bike at a farm near Invercargill. The bike rolled and crashed into a ditch and Charlie died in Southland Hospital as a result of his injuries
• April 2013: Ashlee Shorrock, 6, critically injured when her father Daniel McGregor crashed his overloaded quad bike. McGregor, who had been drinking, was sentenced to nine months' home detention and disqualified from driving for two years after pleading guilty to drink driving and reckless driving charges. Ashlee has since made a full recovery.
• December 2012: Rowan Cai Parker, 16, plunged to his death in South Otago after he lost control of the quad bike he was on and went over a cliff - falling 150 metres on to rocks.
