Kristy decides to form a baby-sitters club with her friends, Claudia, Mary Anne, and Stacy, but they run into unexpected problems which threaten to break up the club.

Stacey, a member of the Baby-sitters Club, struggles with her parents, who refuse to accept that she has diabetes, as she and the other girls in the club deal with baby-sitting problems and a rival baby-sitting club.

Dawn, the newest member of the Baby-sitters Club, gets more than she bargained for when her first job turns into a disaster and she has problems with Kristy.

Claudia's participation in the Baby-sitters Club is curtailed when Grandmother Mimi suffers a stroke and Claudia finds herself "Mimi-sitting" and fighting more frequently with her sister.

During the summer before their seventh-grade year, Kristy, Mary Anne, Claudia, and Stacey tackle difficulties, including family problems, crushes, moving, and making new friends.