|The Rockingdown Mystery by Enid Blyton|
I think it's worth mentioning that Blyton encouraged children to help other children and animals, and to show them kindness. She reasoned that adults are perfectly capable of helping other adults, which I find refreshing.
Another thing Blyton was criticized for was the use of corporal punishment. Children might get a scolding, but if they did something truly wrong they'd get 'a first class whacking'. Her words, not mine.
Although Enid Blyton's books were written for children, I still have a copy of the Rockingdown Mystery, and am tempted to buy the next one in the series.