Should children under 14 years of age have a mobile phone?

I am of two minds. No i don't think so as a lot of the time they are with a person they know, but on the other hand, i do think the child needs one if for example, they are at a fete or fair of somekind, with friends and no adult supervision.( especially the 12 to 14 year olds) Any other opinions. Thank you.