I think an eBook reader for a young girl is a great idea. There are any number of excellent classics available for her -- quite a few have been uploaded here at MobileRead.
Some I can heartily recommend:
- The Anne of Green Gables series by Lucy Maud Montgomery
- Heidi by Joahnna Spyri
- Alice in Wonderland by Lewis Carroll
- Peter Pan by J M Barrie
- Little Women & related series by Louisa May Alcott
- A Little Princess by Frances Hodgson Burnett
- The Wind in the Willows by Kenneth Grahame
As she matures, there are even more wonderful books waiting for her to discover them.
And, over at
Pan MacMillan Ebooks there are any number of children's and young adult books which appear in their catalog -- such as the Princess Diary books by Meg Cabot, Jane Blonde series by Jill Marshall, and many books by Eva Ibbotson.
Outside of the freely available "classics", there are relatively few books available for the Sony Reader. Most of those at the MacMillan site are not yet published in the ePub format used by the Sony Reader.