In his Foreword to Edward Robinson’s The Original Vision, Sir Alister Hardy quotes a verse from Thomas Hood which expresses what is, I suppose, a fairly common feeling:

At least since the time of Wordsworth it has been possible for many people simply to take it for granted that it is this sense of the loss involved in growing up which provides the key to Christ’s saying, “Unless you turn and become like little children you will certainly not enter the kingdom of heaven” (Mt 18:3). Christ’s conditions for entry into the kingdom seem to fall easily into the same pattern as that which we accept readily enough, for instance, in Elizabeth Goudge’s delightful tale, The Valley of Song, in which a variety of respectable ladies and gentlemen shed their years and their cares to find new life in the enchanted Valley. No eyebrows are raised when Peter and Susan are informed that they can never return to Narnia because they are “getting too old” (Prince Caspian, p. 194).