You can use Amazon Kindle books on a kindle, a lap top, a tablet, an ipad or a phone.
All these books can be read for free! There are books for all ages to read and enjoy and if you can't find what you like straight away, you could search under age ranges and be sure to look at the reviews - the more stars the more popular the book.
This is the link you need;
Or type in 'Amazon free kindle books for children'.