I doubt anyone who is enough of a reader to even own a Kindle (or other ereader) would have ZERO hard copies of childrens books for their kids and ONLY buy ebooks. It's not an all or nothing kind of thing. Some people might prefer to have a few kids books on their device for convenience and have the hard books at home.
Another thing is kids see their parents reading on the Kindle and then they WANT a book of their own to read on the Kindle. This argument is like hating a Wii because "Video games are EVIL because kids don't play outside anymore!" ... you CAN have a Wii and it could be played with once a week (or less) ****AND**** play outside
