I have only read this book in (wonderful) Russian translation.
As I don't want to repeat what has already been stated above,
this writeup contains little details about the book itself,
and more about my impressions of it.
I have probably not picked up this book in 20 years, but just being reminded of some of the sequences in it sends me into fits of giggles even now. If you can get your hands on this book, buy it - but don't give it to your kids before reading it yourself! Karlsson is not a desirable role model for your offspring!
To begin with, in my edition at least, Karlsson was not a boy. He was a middle aged, fat little man ("adequately fed and in his prime" is the way he liked to put it) with a receding hairline, who lived away from the prying eyes of society and played with little boys. Ahem. As an artistic outlet he was given to drawing pictures of lonely and deformed red roosters, and his moral outlook was relativistic in the extreme: though not malicious or even greedy in the conventional sense, Karlsson is so supernaturally self-centered that to him, anything that he happens to feel like doing simply cannot be wrong.
When confronted with the consequences of his actions, Karlsson is very much given to dismissing them with a shurg and an utterance - which I am hard pressed to translate into English - something like "oh, but that is a mundane matter". What I take him to have meant by that was that the parents' bourgeois concerns with the intactness if their linen or the non-pilfering of food were petty, overstarched and outmoded; in all imginable ways not applicable to and individualist of such exalted abilities and understanding such as himself: a fine figure of a man in his prime, an accomplished pilot, and a great artist (viz. roosters) to boot. Not that he took himself seriously or anything.
In a way, Karlsson is a lot like Lindgren's other famous heroine - an unstoppable agent of anarchy. But where Pippi Longstocking perpetrates her mayhem through sheer physical force and an undsguised antipathy towards the established order, Karlsson is more the thinking child's imaginary friend. Well spoken, loyal and intelligent, he manages, in his own and his young friend's eyes at least, to almost convey an aura of legitimate political radicalism on their otherwise hairbrained escapades. Give this to your children to read and before you know it you may be presented with a manifesto and a list of demands.
Still, the scene in which the housekeeper (re-christened "housetormentor" by Karlsson for her churlish reluctance to provide an unlimited supply of cinammon Danish and hot chocolate) pursues the giggling Karlsson all over the house, trying to swat him out of the air with a broom like some giant fly is just the funniest thing in a children's book ever. And the book does deal with some very pertinent and serious childhood issues: being the youngest in a busy modern family, having a mother who works and is not there to take care of you when you're sick with the flu, having to stay with a stranger who doesn't care for you and with whom you have nothing to talk about, being lonely in a big city so full of people that it might as well be empty. All this Astrid Lindgren does with great sensitivity, much respect for the reader's intelligence, acutely observed characterisation and of course and above all, oodles and oodles of humour.
In my book, well up there with the best of children's literature.
A note to the confused: Karlsson can become airborn by means of a little propellor sticking out of his back. This he activates by pushing a big red button conveniently protruding out of his belly button - where else?