The figure currently stands at 1,072,328, which is about one quarter of all five- to nine-year-olds. Young phone owners are predicted to rise to more than 1.5 million by 2007.
The figures were revealed last week in a report by MobileYouth, a research consultancy that gathered data from parents, children, mobile phone companies and retailers.
The report also showed many parents are ignoring the potential health risks associated with mobile phones. The average UK child now receives their first mobile at the age of eight, despite 63 per cent of parents expressing concern about the dangers of radiation.
Graham Brown, chief executive of Wireless World Forum, the research company behind the report, said, 'Mobile ownership in the under-tens is predominantly driven by parents. Ninety per cent of parents surveyed in our report cited "child security and safety" as a reason why they purchased the phone. Parents take the view that the benefits of communication outweigh the possible pitfalls.
'The report found the under-tens do not use mobiles excessively and it is very rare for them to contact peers. Most are only using their mobile to speak directly to parents.'
In January this year, Sir William Stewart, chair of the National Radiological Protection Board (NRPB), urged parents to ban under-eights from using mobile phones, in a NRPB report that said children's brains are more vulnerable to their radiation than adults.
However, experts remain divided over the safety of mobile phones. A Danish study, published earlier this month in the journal Neurology, concluded that using a mobile does not increase the risk of developing brain tumours.
But researcher Dr Christoffer Johanson acknowledged there was a lack of long-term data and advised people to use hands-free sets to reduce radiation exposure.