It is a necessity these days. Kids go out with only their friends, come home alone from the bus, etc.
When I was 12, I had to come home alone off the bus, and stay home til my parents got off work. One day, I couldn't get my key to work and I had no way of contacting my parents. The neighbors were not home, and I had no access to a phone. I had to sit outside for 2 hours til my parents got home.
Sure, our parents survived without them, but that was a different time. Kids need cells now for emergencies, yes, need.