How young is too young to have a cellphone and a social media account?

At my workplace I keep seeing tons of little kids (some as young as 6 years of age) with iPhones and iPads and it never fails to shock me. Just a few days ago I was using my company’s internal transportation and there was a family of 6 sitting next to me and they all had their very own latest-generation iPhones. The 4 kids ranged in age from 6 to no older than 11 and they all had Facebook accounts. The whole time everyone had their faces buried in their phones checking their Facebook, Twitter, and Instagram accounts, including the parents.

Does it shock you to see little kids with cellphones or is it just another one of those things that you’ve gotten used to due to its prevalence? Am I overreacting by being shocked or is there really a right age for kids to be introduced to that kind of media? Also, in your opinion, how young is too young to have a Facebook account?