[I]f we are to use the words childish or infantile as terms of disapproval, we must make sure that they refer only to those characteristics of childhood which we become better and happier by outgrowing; not to those which every sane man would keep if he could and which some are fortunate for keeping.
On the bodily level this is sufficiently obvious. We are glad to have outgrown the muscular weakness of childhood; but we envy those who retain its energy, its well-thatched scalp, its easily won sleeps, and its power of rapid recuperation. But surely the same is true on another level? The sooner we cease to be as fickle, as boastful, as jealous, as cruel, as ignorant, and as easily frightened as most children are, the better for us and for our neighbours.
But who in his senses would not keep, if he could, that tireless curiosity, that intensity of imagination, that facility of suspending disbelief, that unspoiled appetite, that readiness to wonder, to pity, and to admire? The process of growing up is to be valued for what we gain, not for what we lose. Not to acquire a taste for the realistic is childish in the bad sense; to have lost the taste for marvels and adventures is no more a matter for congratulation than losing our teeth, our hair, our palate, and finally, our hopes. Why do we hear so much about the defects of immaturity and so little about those of senility?C.S. Lewis, An Experiment in Criticism