The Baby-Sitters Club Kristy's Great Idea: Book 1 by Ann M. Martin

 When Kristy Thomas has the great idea to form a baby-sitters club--a chance to earn money and spend time with her friends, all while doing something they each love to do--she has no idea how much the club will change everything.  Crank calls, uncontrollable toddlers, wild pets, untruthful clients . . . running a business is hard work! Kristy and her co-founders, Mary Anne, Claudia, and Stacey, are sure they can handle anything. But only if they stick together . . .