First, my apologies for taking so long to respond.
Second, unfortunately I don't have Roverandom
and I couldn't find a reference to the tone of The Hobbit
(as opposed to that of LOTR) in the index of Carpenter's biography. I did, however, find numerous references to it in the index of The Letters
. For instance, in Letter 215 Tolkien states:
J.R.R. Tolkien wrote:When I published The Hobbit -hurriedly and without due consideration - I was still influenced by the convention that 'fairy-stories' are naturally directed to children .... it had some unfortunate effects on the mode of expression and narrative method, which if I had not been rushed, I should have corrected.
Various forms of this appear in a number of other letters, and in most of them Tolkien expresses his regret with the extent to which he aimed The Hobbit
at children (or at least, that he did so in the normal way of the time). However, regardless of his later regrets, it's fairly certain that The Hobbit is
in fact a book for children, whereas Tolkien's other writings are not. However, regardless of the label (or lack thereof) "children's book", his writings can still be read and enjoyed by people of many different ages.