They warn that a huge selection of mobile-phone toy accessories and 'wallpaper', including Jetsons screensavers and Toy Story ringtones, are encouraging children as young as four to use handsets.

Phil Willis, chairman of the House of Commons Science and Technology committee, this weekend called on the department of health to launch an urgent inquiry into the cartoon marketing of mobile accessories to children. He said the issue was potentially as serious as the marketing of junk food and sugary drinks to primary school students.

Hundreds of mobile phone accessories attractive to children are being sold in mobile phone shops and via the internet.

The MP warned that the British government was in danger of breaching its own guidelines on the use of mobile phones for young children, which says they should be used infrequently to ensure there are no possible health risks.

He said selling cartoon merchandise was irresponsible after experts warned that caution should be exercised when giving mobile phones to young children. They urged a "precautionary approach" because children have thinner skulls and developing brains.

John Carr, of the children's charity NCH, said he was concerned that while service providers such as Vodafone were observing a voluntary agreement not to market phones to children, other companies were cashing in with cartoon mobile phone accessories.

"The mobile phone companies have been rigorous in not marketing to children. But it's bizarre and odd that the phone providers are accepting a very high level of restraint but nobody else seems to, " he said.

Hundreds of accessories that appeal to children are available in mobile phone shops and over the internet and the average age at which children now receive their first mobile is eight. Ninety per cent of schoolchildren between the ages of 13 and 14 carry handsets.

Companies such as Disney and Warner Brothers market a large selection of cartoon ringtones, wallpaper and accessories, including Winnie the Pooh and Scooby Doo ring tones. Disney is considering starting a mobile phone company, aimed at families, in Britain.

An official inquiry into the safety of mobile phones recommended not giving mobile phones to children under eight.

A spokesman for Disney yesterday said the company always acted responsibly, and was considering developing a Disney branded mobile phone service for families in the US and elsewhere.

"We are looking at family product options that would uphold the high standards of the Disney brand and include features attractive to families such as parental controls, among others, " said a spokeswoman.