I don't think they should, because I can't think of a situation where they would need one. When they are under ten, they are probably not going out by themselves! If there is an emergency at school, the school will call you. If they are at a friend's house, the friend's parent/guardian can call you if needed. I don't think someone this young should be left alone at shopping centres, the cinema etc. If your child is travelling by him/herself to and from school, then this would be a situation where he/she might need one. Otherwise I don't think it's necessary.