I just can't see that age-banding on the backs of books will actually persuade people who don't buy books (for children) to go out and buy them.
From another English commenter:
From my years of sales experience at Walker Books I found all level of age banding on shelves, displays, removable stickers simply did not achieve a great result. The majority of booksellers in the large stores would run a mile to avoid 'that messy kids section'!
Which left me feeling that my sense that booksellers often undercook the kids section was absolutely right.