Most accident victims were playing with others on the trampoline
Trampoline accidents are increasing and parents are ignoring safety advice, according to doctors.
Doctors at Kingston Hospital in Surrey say they have seen a surge in the number of children they treat for accidents on a trampoline.
Between May and September of last year they treated more than 130 children for fractures and cuts.
The Royal Society for the Prevention of Accidents (ROSPA) says parents must follow the manufacturer's advice.
Writing in the Emergency Medicine Journal, the doctors at Kingston say parents need greater awareness of the dangers.
More than half of the 131 children treated at the hospital's emergency department last summer had no nets on their trampoline and no adult supervision.
The commonest injury was a soft tissue sprain followed by fractures, head injury and cuts.
Select the right size equipment
Site it away from obstructions like fences
Properly supervise the children
Ideally allow only one person on at a time
Most had been playing on the trampoline with other people at the time of their accident.
Operations were carried out on 18 children and 28 were referred to a fracture or ear nose and throat clinic.
The average age of the children was 8.8 years and 92 (70%) were boys.
Dr Dan Harris, who led the research, said he had been surprised by how significant some of the injuries were.
He said: "It's difficult because I can see lots of trampolines in gardens in the Kingston area and clearly only a small percentage of the children are getting injured but some of those injuries are life-changing fractures which will cause continual joint problems."
A fifth of the injuries were in children under five who had been playing on large trampolines of more than 10 feet in diameter.
They were with an average of 2.7 other people on the trampoline which the Kingston doctors said was especially hazardous as the lightest person on the apparatus was five to 14 times more likely to be injured.
This happens through a phenomenon called "kipping" where synchronous jumping - jumping at the same time - causes the transfer of kinetic energy to the lightest person causing them to gain greater propulsive force and height.
Asynchronous jumping would cause less skilled jumpers to be propelled at unplanned angles, resulting in collisions and misplaced landings.
About a third of the children (42) were injured after purposely jumping from the trampoline or accidentally falling off it.
The Kingston doctors took careful records of how the accidents occurred.
These show that where netting and padding was in place on the trampoline adults were often lured into a false sense of security and left the children unsupervised which in turn led to more risk-taking activities and more injuries.
The Kingston doctors followed up 90% of the patients with a call and found that 115 had continued to use the trampoline after or, in some cases, during their recovery phase.
However, all 119 parents reported that their own attitude to supervision and allowing several children on at the same time had changed.
Dr Harris said: "Unfortunately, for all them it took an injury to their child to initiate such change."
The Royal Society for the Prevention of Accidents said the government had stopped collecting accident statistics in 2002 and so studies like this were particularly valuable.
Jo Stagg, from ROSPA, said: "Trampolines can be enjoyed safely if you follow some simple guidelines.
"Parents should read the information that comes with the trampoline because it's there for a reason."
Dr John Heyworth, of the College of Emergency Medicine, said the numbers of trampolines seemed to have exploded in recent years and the number of injuries from them around the UK was continuing to rise.
He said: "Parents need to make sure the fun is harmless - it's common sense - follow the recommended guidelines and children can still let off steam safely."