I saw one mother on the "Today" show talking about cell phones and kids. She took her son's cell phone away and he said "Mom, without my cell phone I have no life."
I thought that was really scary.
I see no reason for kids that young to have a cell phone. Another "Today" show moment had this poll. I don't remember the age or percentage, but it showed more young kids of a certain age knew how to download an app, but didn't know how to tie their own shoes.