"When they were admitted to hospital last night we took blood samples of all four adults for analysis, and there may well be charges pending as a result," Mr Shadbolt said.
"Last night it was unclear who was actually driving."
He said quad bikes were subject to the same laws as any other vehicle travelling on a public road, and those driving them needed to be cautious.
"Quad bikes are an important part of the rural life in New Zealand, a vital tool on farms and used around beaches. But we know there are dangers for them," Mr Shadbolt said.
"This one is ... right outside the parameters of what you'd call normal or reasonable use.
"It was just stupidity."
The girl's father was flown to Hawkes Bay Hospital with a badly broken leg.
The other three adults were taken to hospital by ambulance with dislocated hips, broken legs, broken arms and suspected head injuries.
Waimarama Volunteer Fire Officers and police based at the beach for the holiday period initially helped at the scene, along with St John ambulance staff.
Federated Farmers' spokeswoman Jeanette Maxwell said farmers were taking quad bike safety seriously, but the message was not getting through to recreational users.
"There is an unhelpful assumption all quad bike accidents are farm related ... and this recreational toll is a concern," she said.
If an untrained person wanted to use a quad bike they had to seek training, she said.
"The Ministry of Business, Innovation and Employment needs to look at how it is communicating safety messages to casual quad bike users. Frankly, no one should be using a quad bike without the appropriate training and not all quad bikes are designed to carry two people."
