Dd had one at about seven years old, it was one of my old ones and she used it as an iPod and for daft games and a few messages to my mum. No way would she have been allowed to take it to school though.
DDs had (supervised) access to the Internet from toddlerhood and then iPad at about 9 and she now has a phone that she takes to school with her (y7) but is switched off in her bag all day. A lot of work in y5 and y6 at school was based around iPad usage and now in y7 the students have to create an iPad app, I do think that her having access to this stuff outside of school has helped with her understand of they work in a way using them only at school may not.
There's so many things you can do with technology and it's not always games and Facebook, there's apps that help with revision for SATs and exams, creating music, editing videos to make movies for school projects etc and if used correctly iPads and smartphones can be a good extra for learning.
my sil has said she has just gave my nephew a phone at 10 for Christmas and she wished she phased it over a year or so rather than handing him one with a list of rules. It's all new to him and in his excitement and wanting to okay in it, he forgets some of the conditions.
DDs has the safety stuff drummed into over years so didn't have to take it all in in one go type thing. She uses her Phone for homework (quite a bit has to be submitted online) and reading school textbooks etc.
There's no right or wrong and I totally understand why many parents want to wait before giving their DC phones and tablets etc, was just posting to say that there's nothing wrong in little ones having them provided they are supervised correctly.
I know one of the boys in DDs class was viewing porn on his opine at six years old, I used to be friends with his mum and she was clueless about technology but rather than teach herself the basics of how to set up filters, monitor his usage etc, she blamed the phone company and didn't confiscate or monitor internet usage and let him carry on viewing it. That boy now has some very worrying attitudes and behaviours around girls and I'm convinced him watching abusive porn from such a young age has played a part.
Some DC are totally fine from a young age, and some are not. Parents have to choose what they feel best for their DC.