Swallowdale

Well... I don't know if I should put up a warning for animal abuse or not... it's not that obvious.
But they do treat the poor parrot abominably. Parrots are very intelligent and social animals, and shouldn't be left alone for a long time. It also felt that the poor thing had nothing to do but sit in its cage, and also I believe its wings were amputated. Not just feathers clipped, but her arms were cut so that she couldn't fly.
Also, the adder living in a box... er... uh.

Anyway, it's a good book about the adventures of children in the 20s and 30s. I especially appreciate equality. John is not the best captain because he's a boy. Nancy is just as good, and in some aspects better. Susan is a “good housewife”, but also an apt shipmate. The gender of people never comes up as an issue.
I also love the fact that all adults are good people. There is no “stranger danger” here. Everyone is friendly, generous, and kind to the kids.
And, it's not ageist. The children are not belittled or not listened to just because they are younger. Everyone is treated with respect.