The truly great children's books contain a hint of darkness or a twisted sensibility (eg. the Roald Dahl books like Charlie and the Chocolate Factory & James and the Giant Peach, the Series of Unfortunate Events books, and the Harry Potter series) which the children must overcome.
Though I was pleased by the inclusion of a runaway dirigible and a floating house I thought this book maybe lacked that hint of darkness...but then a Nazi concentration camp director shows up as overlord of a native African village filled with domesticated East Indian tigers.
I've owned my copy of this since 1979 according to the inscription. I don't think it's aged too badly, either, considering.
Jane's a great child protagonist, convincing and practical, and the adventures she has, along with Mrs Deal, her family's housekeeper, as they're both swept away in the airship her father has built, are pretty exciting, moving from avalanches in Switzerland to escaped Nazis in Africa.
I'm adding this one now because I've just pulled it off a dusty old shelf to read to my children. It's great for either boys or girls, reading it to them from about five or reading themselves a little older. I suppose it'll be a little old fashioned compared to the subject matter of current children's books but it has some fabulous characters, a great romp of an adventure and some really wonderful comedy. I'm enjoying it all these years later and theses sorts of classic children's tales really don't age. It's about a girl who is whisked off in a house attached to a hot air balloon to escape natural disasters and tyrants...what more could you possibly want? Thoroughly recommended.