"Even in peacetime I think those are very wrong who say that schoolboys should be encouraged to read the newspapers. Nearly all that a boy reads there in his teens will be known before he is twenty to have been false in emphasis and interpretation, if not in fact as well, and most of it will have lost all importance. Most of what he remembers he will therefore have to unlearn; and he will probably have acquired an incurable taste for vulgarity and sensationalism and the fatal habit of fluttering from paragraph to paragraph to learn how an actress has been divorced in California, a train derailed in France, and quadruplets born in New Zealand."First, I notice that the news paper -- or news in general -- hasn't changed since his time. More important, though, is his observation about the time of school children.
School is a time to learn Truth and to develop tools for continued learning: reading -- not the news but reading in general and the reading of good literature, mathematics (arithmetic), and catechism. These are the core languages for further study, without which you can't progress is anything that follows from them. Truth can be find in many fields--in literature, in history, in math--and any real truth points, in some way, to He who is Truth. A few pages earlier, Lewis wrote that "...the true training for anything whatever that is good always prefigures and, if submitted to, will always help us in the true training for the Christian life."
School is also a wonderful (literally) time to have one's imagination baptized. What baptized Lewis' imagination? By his own words, in my favorite section of the book, it happened when he read George MacDonald's Phantastes. More broadly, it was baptized by good fantasy, like MacDonald's (and good fantasy is an act of sub-creation, an act in the image of God). It was baptized by mythology, the "good dreams" given to earlier mankind. It was baptized by fairy stories, where, in the best, you find wonder, morality, and an omnipresence of God; where all things are heavy with significance.
Aren't these things childish? Not at all. But they are first for children. Don't forget, though, that we're told to be child-like (c.f. Mt 18:3), a command that seems applicable to our reading as well. And why shouldn't it, when we're told to be child-like in spirit, and what we read feeds our minds and souls. It goes into that spirit and, therefore, should be fit for a child (and a child of God).