The 122-book series centered on seven-year-old Karen Brewer, the stepsister to Kristy Thomas, who is the President of the Baby-Sitters Club.
Karen usually tries to do the right thing, but because she has been through some hard times in her young life, she sometimes makes a mistake.
In the beginning of the series, Karen and her younger brother, Andrew, live primarily with their mother, Lisa, and stepfather, Seth Engle.
Karen and Andrew do not get to spend much time with their father, Watson Brewer, and stepmother, Elizabeth Thomas-Brewer.
On April 30, 2019, it was announced that there were plans for a series of Baby-Sitters Little Sister graphic novels illustrated by Katy Farina and colored by Braden Lamb.