Sadie and Ratz by Sonya Hartnett.

Sadie and Ratz are the names of Hannah’s hands. They aren’t animals, but they behave like wild beasts. For one thing, they’re always after four-year-old Baby Boy. Baby Boy knows how to turn the tables, though, and when he blames Sadie and Ratz for trouble he causes, Hannah may have to send Sadie and Ratz on vacation to prove their innocence.