You can't accuse C.S. Lewis of talking down to children. The Chronicles of Narnia are serious books; I remember in childhood being rather in awe of them.
It's also very clearly, from an adult point of view, a biblical allegory about the crucifixion, something I totally missed as a child, of course.
Narnia is a fantasy, fairy tale world of magic spells, fauns, unicorns, giants, ghouls and ogres, famously reached through a wardrobe by four children. The White Witch, who has made it permanent winter in Narnia, is seriously nasty, and then of course there's Aslan, the mighty lion saviour of the realm. Even Father Christmas makes an appearance.
It sounds a bit of a folklore/mythology/religion hodge-podge, but it works - this is an emotional, at times heart-rending read. The tone of seriousness begins, for me, when we realise that the younger brother in the family, Edmund, is a spiteful and selfish Judas, tempted to endanger his siblings so that he can become king and eat magical Turkish delight.
C.S. Lewis's revelations of brutal evil on the part of the White Witch, and the willing suffering of Aslan for Edmund, are really quite upsetting at times. What a relief that Edmund turns out to be a good person in the end, having learned his lesson.
For me, the best part is the time shift at the end of the book when suddenly many years go by and the children grow up in Narnia to become like medieval royals speaking courtly English.
Delightfully, Edmund is now Edmund the Just, a quiet, grave man, 'great in council and judgement'. And then within just a few lines, they stumble across the lamppost that leads to the wardrobe they have all but forgotten, and tumble back out into wartime England as children once again, having lost not a minute. Best of all, their grown-up friend, the Professor, believes everything they tell him - the world of Narnia is to be taken seriously.
Interestingly, the order of the series of Narnia books is far from established. The Lion, The Witch and The Wardrobe was the first to be published, while the prequel to its events, The Magician's Nephew (also a wonderful read) was one of the last - scholars argue over which should be read first. The Lion, The Witch and The Wardrobe is certainly a good place to start, though.
Clive Staples Lewis was an academic, committed Christian, and medievalist who taught English at Oxford and Cambridge universities. He was a good friend of J.R.R. Tolkien, the author of The Hobbit and The Lord of the Rings.
The Narnia books were written between 1949 and 1954, but Lewis is also remembered for his books for adults, especially on theology. Born in Belfast in 1898, he died in 1963 in Oxford. The Narnia books have sold over 100 million copies in 47 languages.