My 10 year old has had a Kindle for about two years now. He shares a room with his younger brother and was running out of places to store his books. His dad got fed up with all the books laying around and bought him a Kindle Touch.
He takes around with him pretty much everywhere and, in typical boy fashion, leaves it laying around pretty much everywhere as well. He still has the original case that we bought with it -- it looks quite a bit worn -- and is on his second M-Edge e-Luminator Touch light. The Kindle itself is in good condition.
He was not allowed to have it in class when he was in third grade, was encouraged to bring it in fourth grade, and it is again not allowed to bring it in fifth grade. (All by the teacher's discretion; I do not believe there is an official school policy.)
My husband saw a deal on an older model Kindle (third gen, with keyboard) and bought it for our daughter. She is only seven years old now, and has no interest in reading. What little reading she does, she prefers to do on paper books, although there are a couple of stories on the Kindle that she has enjoyed. I don't believe she has ever finished an entire chapter book, although she has started quite a lot of them.
My five year old does not (yet) have a dedicated ebook reader.
All three of my kids have Kindle Fires with the
Scholastic Storia app and a dozen or so books each. The books are kind of expensive -- comparable in price to the paper versions sold in the flyers -- and I don't see any way to read them outside of the app, so I don't buy very many books from the store. They count toward classroom purchases, so I do buy books now and then because of that.