Mobile phone firms are cynically targeting children despite fears they are most at risk from radiation, a leading scientist claimed yesterday. Sir William Stewart who led the world's biggest investigation into mobile phone safety, said those who encourage under-16's to buy handsets were irresponsible. The warnings came at the same time that the British government announced they are spending 7.5 million pounds to continue research into cell phone safety. Children's brains are thought to be particularly vulnerable to mobile phone radiation because their skulls are thinner than adults. As many as nine in ten British teenagers are thought to own mobile phones.