I have never 'studied' it but believe it to be about never allowing yourself to stop viewing the world with childlike wonder. It reminds me a lot of this poem which is one of my favourites.
I think it is about remaining open-minded and imaginative and not allowing oneself to become rigid in thought and to conform too much. I guess that we should keep wondering and searching and not think we have all the answers.
Funnily enough I was talking to DD about this book less than an hour ago! Someone just bought it for her for a confirmation present - she is 13. I was asking her what it was about and she seemed to think it was to do with not worrying about the little things.
On another French (or rather Belgian) topic - there is a new DVD version of the Tintin books out right now, they are fabulous - three stories per DVD, there are 7 or 8 DVDs in total in the new series. DD is hooked. Each DVD is multilingual.
I read it in English as a young child, in French as a teenager, and again (and again, and again) as an adult. I've loved it each time, and each time I've found something new in it.
You can enjoy it for the rhythm of the language, the illustrations, the strangeness, the superficial story...or you can look for deeper meaning. I think it's one of those rare books from which you take whatever you want - there's no 'right way' to understand or interpret it.