The best reader for children is...
Yes, I agree with jereese. Read to them while they are young with paper books. Because once you get the e-reader it will be used as a game player. I'm a school bus driver and I have elementary school age children that own Iphones, Ipods, smartphones and other electronic devices; they are not using them to read any kind of book.
Their eyes are constantly on the gadget. The kids have better phones than I have. But enough of that rant.
My oldest son loved when I read to him.He had his favorite book, sadly I miss those simpler times. He is going to be 21. He forgot about his favorite book.I reminded him of the book, he smiled," yes it was a nice book Mom".
So yes, get a library card and get the old fashioned readers, a book.
The Library is free, and it's fun. It will give you and your nephews some great memories to share together.