Some people consider this a children's book. After all, Kenneth Grahame wrote it for his children (or so he said).
I wasn't exposed to it until I was 28 years old -- 1980. It was an early autumn afternoon. I was listening to the radio -- the local university station, with a tie-in to NPR. The actor David McCallum was reading chapters from the book. I didn't know what hit me! There's no way to describe the fantastical mood I was cast into. Mes-mer-ized.
When I soon got my hands on the actual book, army tanks and bazookas could not have pried it from my hands. This book is almost too much of a good thing for me. I've not recovered since.