Three of Australia's leading children's hospitals have published a joint statement that examines whether anaesthesia affects a child's developing brain.

A child exposed to general anaesthesia for less than three hours just once before the age of three is not at increased risk of learning disabilities, parents have been assured.

Three of Australia's leading children's hospitals have published a joint statement that examines whether anaesthesia affects a child's developing brain, based on the past two decades of evidence.

It comes after a "worrying" study, published last month, found an association between multiple exposures to prolonged general anaesthesia and lower NAPLAN scores among a group of 210,000 Year 3 students in NSW between 2009-2014.

Paediatric anaesthetist Dr Jonathan de Lima of The Children's Hospital, Westmead says prior to the study anaesthetists were rarely asked by parents, perhaps a dozen times a year, if the anaesthesia would harm their child's developing brain.

He hopes the statement, which took in five recent epidemiological studies involving hundreds of thousands of children including every child born in Sweden over a 20-year period, will help to reassure parents anxious or concerned about their children's operations.

According to the statement, a single exposure to anaesthetic drugs of less than three hours before three years of age does not lead to reduced developmental scores.

"A single brief anaesthesia does not appear to lead to a reduction in neuro-cognitive outcome," Dr de Lima said while speaking on Tuesday at the Australian and New Zealand College of Anaesthetists' annual scientific meeting in Sydney.

Multiple exposure to anaesthesia, however, does appear to be more problematic.

"Neuro-cognitive decrements are associated with multiple surgeries requiring the anaesthesia," said Dr de Lima.

This does not prove a causal effect, he stressed.

The expert also said overall the effect of multiple prolonged exposures to anaesthesia on a child's academic achievement is "very small".

"Even month of birth has more effect on your academic achievement and IQ than does exposure to anaesthesia," said Dr de Lima.

The surgery, anaesthesia and pain statement can be found at http://www.schn.health.nsw.gov.au