Experts want a new safety standard brought in to control trampolines, which are associated with more than 1000 injuries a month, according to ACC data.
Seventy-eight per cent of the trampoline injury claims made to the Accident Compensation Corporation involve children aged 14 or younger.
The number of head injuries associated with trampolines increased by 289 per cent from 2013/14 to 2017/18.
In the same period, neck injuries rose by 33 per cent and lumbar and thoracic spinal injuries rose by 29 per cent.
ACC's annual cost of treatment for trampoline injuries rose from $4.2 million, to $8.9 million; the average cost per patient rose from $443, to $683.
Canterbury University engineer Professor Keith Alexander and Consumer NZ want a new standard introduced for trampolines.
Alexander said the standards covering trampolines were withdrawn in 2014. It was suggested they would be replaced by the Australian standard, but that hadn't happened.
"In their absence we have seen a flood of sub-standard imports enter the New Zealand market that are frankly quite hazardous for our children."
Nets failed from UV light within months and padding in many cases came off in the first year of use and wasn't replaced.
"This leaves a comparatively dangerous product in the back yard."
He urged that New Zealand adopt the Australian standard AS4989 and make it mandatory.
Consumer's head of testing Paul Smith said the organisation's tests of trampolines found that all except the one invented by Alexander failed basic safety testing based on the former New Zealand standard.
Emergency Department specialist Dr Vicki Vertongen, of Wellington Hospital, said children needed to be active, but they also needed to be safe and on a trampoline that included having good nets that were zipped up.
"We are seeing a number of children in the Emergency Department who have fallen off trampolines without nets. They often present with fractures, particularly of the arm and also head injuries - which can range from mild concussion to a more significant head injury that requires hospitalisation."