Mallory and the Trouble with Twins (The Baby Sitters Club Series #21)

Mallory knows she's a good baby-sitter. She's been looking after her seven younger brothers and sisters for years. So when Kristy offers her a steady job baby-sitting for the Arnold twins, Mal thinks it'll be easy money. The twins are cute in their little matching outfits. But once Mrs. Arnold leaves, Marilyn and Carolyn turn into twin terrors!