Generic-but-good girl series, where the girls do lots of adventurous things and are way cooler than the boys, and very matter-of-fact. I liked it a bit as a kid, though I mostly read it for lack of other things to read. I can still name some of the characters and their general vibe (ok, mostly Sprotte), which is a mark in favour of the book.
As the English title of this book is “The Summer Gang”, it pairs unsurprisingly well with Enid Blyton.