i've tried my cell phone, tablet 10 inch), and kindle to read ebooks. i found that kindle is the best. but this is for fiction. for books containing spectcular pictures and children's books, i still like real books.
I d/l some books to iPad. But the audio and little games are so attractive, my daughter would not listen to the story. She would use the home button to switch to kid song and video. So I buy a lot of English from Taobao. She also enjoy story telling and asking question. She is just 3 now.
I won't let my son use any electronic device. Using electronic devices for study may become the trend in the future, reading paper book is still the best.