The effect of mobile phones on children has, until now, remained untested. Australian scientists are investigating if children are more vulnerable than adults to the effects of radiation from mobile phones.

A study of 110 adults at the Australian Centre for Radiofrequency Bioeffects Research, partly funded by the Federal Government, confirmed mobile phones cause a change in brain function by altering brainwaves known as alpha waves.

The centre, at Melbourne's Swinburne University of Technology, is now investigating the effect on 40 children aged 12 to 13, and 20 people aged 55 to 75 years.

Associate Professor Rodney Croft, from the centre, said while studies had been conducted on adults, the effect on children had, until now, remained untested.

"Although there's a tiny effect on healthy young adults, there is a possibility that it could be much stronger in children or the elderly," Professor Rodney Croft said.

There was no indication from the adult tests if the effect on health was positive or negative.

Scientists worldwide agree there is no evidence linking electromagnetic radiation emitted by mobile phones to adverse health effects, but claims that frequent use can cause headaches, nausea, problems with concentration, cancer and brain tumours still persist.

The new Australian study comes as France's health ministry warned parents to prevent children using mobiles when reception is poor or during high-speed travel.

Authorities in France advised limiting the use of mobiles overall.

Last week the National Research Council of US called for more studies into the possible health hazards of wireless devices and base stations on children, unborn babies and pregnant women.

Researchers fear children may be more vulnerable because the exposure dose received by a child's brain is higher than an adult's and their nervous system is still developing.

With one in four Australians aged six to 13 now having a mobile phone, children will also be exposed to radiation for longer than their parents.

A British study noted many cancers take 10 to 15 years to appear, and most testing so far had included few participants who had used mobile phones for longer than a decade.

Professor Croft said Australian studies using unborn or newborn mice had failed to find significant changes in growth rate, brain function and behavioural development.

The professor of public health at the University of Sydney, Bruce Armstrong, said the French decision against excessive use by children was prudent.

"We don't know that use of mobile phones causes harm to children but we don't know with certainty that it is safe in all circumstances," he said.

A spokesman for federal Health Minister Nicola Roxon said: "We have no plans to restrict usage at this point. Of course we monitor any developments in medical research as a matter of course."