The Baby Sitters Club was a series of books by Anne Marie Martin designed for elementary school girls about a club of junior high girls who baby sit.
Much like the Goosebumps series, the books would come out every few months, and each would bear a number as well as a title. The books were usually around 120 pages or so, and were broken down into a dozen chapters.
The books revolved around the members of the Baby Sitters Club, of which there was anywhere from 4 to 7, and what they did, which was mostly baby sit and get in fights with each other. Each member of the Baby Sitters Club had a different personality, all of which were fairly stereotypical...there was a loud mouthed tomboy; a blonde who was into boys and a shy, quiet girl for example.
Despite the fact that the books did not go into the greatest psychological and philosophical depths, they were quite quality literature, if you were a third grade girl who wanted to know what life was like in the glamourous middle school years.
Although I refer to these books in the past tense, I should point out that, as far as I know, after about 150 volumes, they are still being published.
Although these books were intended for pre-adolescent females, I read them quite a bit during the summer when I was 17, but I was also drinking a lot of methanol at the time.