Arthur Ransome's 1930s Swallows and Amazons series is really less a group of novels, and more a multi-volumed set of instructions on how to properly conduct summer (and occasionally winter) vacations.
These British get-inside-a-kid's-head books span both genders, and, although sometimes bogged-down in tedious detail, are full of innocent childhood independence, adventure, and wit. Think of them as a cerebral, and lengthy, Boxcar Children series.
The Swallows and Amazons series by Arthur Ransome is featured in Vol 7 No 5 of The Storybook Home Journal.