Among more than 800 parents and carers whose children presented at one of three emergency pediatric emergency departments in the first half of 2015, nearly half said the patients had used alternative treatments in the previous 12 months.

Only 20 per cent of those who had used an alternative therapy in the past week had told their doctor.

The most common treatments were massage and chiropractic therapy, and they also included aromatherapy, osteopathic manipulation, homeopathy, kinesiology and hypnosis.

Study author David Taylor, who will present the results at the annual scientific meeting of the Australasian College of Emergency Medicine in Brisbane on Wednesday, said there was a risk that these therapies were interacting harmfully with the treatment plan given by their doctors or that parents who used alternative therapies on their children were delaying conventional treatment.

He recalled one of his patients, who was not part of the study, who presented at his emergency department with a painful hip - found on x-ray to be the result of a slipped femur.

It emerged that she had been visiting a chiropractor over the previous several months, during which time a condition that could have been treated with early detection had deteriorated beyond repair.

"This was a beautiful nine-year-old girl and she was going to have terrible, terrible arthritis for the rest of her life and a hip replacement in her twenties because she had chiropractic treatment without an x-ray," said Professor Taylor, who is director of emergency medicine research at Austin Hospital in Melbourne.

Common reasons for alternative therapies were musculoskeletal pain, stiffness and injury, general health and wellbeing, upper respiratory tract infections and relief of anxiety.

Nearly 60 per cent of those who used alternative therapies them believed them to be safe, but only seven per cent of those who used them believed them to be more effective than prescription medicine.

Nine adverse events were reported.

Children's Hospital at Westmead toxicologist Naren Gunja said patients should always disclose to their treating doctors if they were taking an alternative medicine, as these had the potential to interfere with pharmacy or regular medicines.

"There are known interactions and some of these can cause people to become sick," Associate Professor Gunja said.

"And there are alternative medicines that are potentially harmful and haven't been tested, so they need to be open about that."

These included chelation for people who believed they had heavy metal poisoning, which could cause fevers, vomiting and diarrhea, and laetrile for people seeking a cure for cancer, which could could cyanide poisoning when taken in large amounts.