Parents should ensure their children use mobile phones only when absolutely necessary because of the potential health risks, an expert is warning.
Many children use mobile phones
The latest study by Sir William Stewart says there is still no proof mobile phones are unsafe, but warns precautionary steps should be taken.
Sir William said children under eight should not use mobile phones at all.
In light of the findings, a phone designed for this age group has been withdrawn from sale in the UK.
The MyMo phone went on sale five months ago aimed at four to eight-year-olds to use in an emergency.
But in a statement, the UK distributor Communic8 said: "Although we feel the product, if used as recommended with parental guidance, is safe, we are not experts in either the radiation or medical fields that Sir William and his team are.
"Simple common sense has convinced us that even the remotest possibility of our product becoming a health risk to any child is unacceptable."
Sir William, now of the National Radiological Protection Board, first warned five years ago that children should only use mobiles in emergencies.
But he is now concerned that advice is being ignored.
Mobile phone operators welcomed the fact that Sir William's report highlighted the lack of hard evidence linking handsets with adverse health effects.
One in four seven to 10-year-olds now own a mobile phone - double the levels in 2001, according to latest figures.
Sir William's new report, published on Tuesday, warns that if mobile phones do damage health, then children will inevitably be at greatest risk.
It also calls for a review of the planning process for base stations.
Sir William said he did not favour mobile phone masts being situated near schools.
He told the BBC Radio Four Today programme there was no absolute evidence that mobile phones were a risk to health - but various studies had raised serious concerns.
Youngest at most risk
He said: "If there are risks - and we think that maybe there are - then the people who are going to be most affected are children, and the younger the children, the greater the danger.
"Parents have a responsibility to their children not simply to throw a mobile phone to a young child, and say 'off you go'."
Professor Lawrie Challis, who was vice chairman of the Stewart Inquiry and is now chairman of the Mobile Telecommunications and Health Research programme, set up to investigate the health risks of mobile phones, told BBC News: "I would certainly not wish my own grandchildren to use mobile phones more than they had to."
Rosie Winterton, the Public Health Minister, said government guidance stressed that mobile phones should not be over-used by young children.
"Obviously there are parents who feel they want to children to have mobile phones for safety reasons, but we are quite clear that they ought to be very careful about over-use.
"There is on-going research both in the use of mobile phones and the siting of mobile phone bases."
Since the first Stewart report experts have remained divided over whether the phones pose a risk.
Last year a 750-people study by Sweden's Karolinska Institute suggested using a mobile phone for 10 years or more increases the risk of ear tumours by four times.
A Dutch study has suggested mobile phone use can affect brain function, and further research from Europe indicated radiation from the phones can cause DNA damage.
But Dr Adam Burgess, a lecturer in sociology at Kent University, published research a year ago dismissing claims mobile phones were harmful.
He said: "I do not know why these latest warnings are being made, they are exactly the same as was said five years ago.
"As far as I am concerned mobile phones are safe to use.
"There may be some unknown risk that could appear at some unknown date in the future but we have to balance that against the benefits of using them."
And Mike Dolan, executive director of the Mobile Operators Association, said there were good reasons why children carried mobile phones.
"Families do go out there and purchase mobile phones for their children very often for very tangible security benefits.
"Parents have to weigh that benefit against any possible unknown health effects in the future."