Babysitting Is a Dangerous Job by Willo Davis Roberts, 1987.
Thirteen-year-old Darcy knows that babysitting the Foster kids isn’t going to be easy. Jeremy, Melissa, and Shana Foster are young children and rather spoiled. Their parents are wealthy, but they don’t spend much time with their children. When Darcy babysits them, the children go off in different directions and do things they know they aren’t supposed to do.
On top of that, Darcy is worried that someone will figure out that she and her friend Irene have been helping to hide their friend Diana, who ran away from home because her father was beating her. Diana is afraid to go to the police because her sister tried to tell them about their father’s abusive behavior, and no one believed her. She thinks that the police will just take her home and her father will beat her again.
One day, while Darcy is babysitting the Foster kids, some men break into the house and kidnap them all for ransom. Darcy feels guilty for not preventing the kidnapping, but she’s determined to make sure that she and the kids make it home safely to their parents. When the kidnappers make a slip that allows Darcy to discover their true identity, she must come up with a daring plan to save herself and the children, who turn out to be surprisingly resourceful themselves.