Back to the subject... I was one of those weird kids who read everything in the children's section of the library (I presume most people actually remember libraries back when they had books in them...) before I was 10 and was given a special (secret) adult library card... so I was reading all kinds of things pretty young. I got in trouble for ordering the Marquis de Sade from the school bookshop when I was 13, but in the end they still let me have it - all I can say is, if you think James Bond was eye-opening...
So when I think of kids' books, much of what I'm really thinking of (and indeed what's already been mentioned here) would now be called Young Adult books... I loved Susan Cooper's The Dark is Rising sequence, Lloyd Alexander and Alan Garner (already mentioned), Leon Garfield, John Christopher... Peter Dickinson was a major favourite - I loved The Changes sequence, Tulku and others - he's still writing, apparently - Tolkein and Lewis natch, Ursula Le Guin's Earthsea books, which she has continued to write sporadically and which have grown up with her audience - the last book, The Other Wind is a beautifully moving adult work, but it is still absolutely and unequivocally Earthsea. I also loved the bits and pieces that I came across from other places - one of my favourite books was a kid's novel from New Zealand, The Boys of Puhawai, which just seemed incredibly exotic but also very real indeed. I read lots of mythology too, from Norse myths to Chinese tales... I could go one forever. I still get lost in books. My wife only really read non-fiction. I don't get it.