The youngest Pevensie sibling in C.S. Lewis’s Narnia books is Lucy Pevensie.
Lucy is introduced in The Lion, the Witch and the Wardrobe, first published in 1950. She discovers the passage into Narnia through the wardrobe and becomes the first of her siblings to enter that world. Her name is Lucy, and she is the youngest of Peter, Susan, Edmund, and Lucy.
Lewis portrays Lucy as courageous, truthful, compassionate, and spiritually perceptive. Her willingness to trust what she has seen is central to the first book, especially when her older siblings initially doubt her account of Narnia. She later appears in several further Narnia stories.
Susan is Lucy’s older sister, while Jill Pole and Polly Plummer are separate Narnia characters. This distinction matters because the series includes several young heroines whose adventures overlap, but only Lucy belongs to the Pevensie family.