Fear

"In one home where simple and direct explanations were to be had for the asking, a boy of three watched in silence as his baby sister was being bathed. It was evident from his expression that he was troubled by what he saw, now that he was face to face with the fact that there was a human creature who lacked what he had and prized. He did not comment on what he saw, but he became more and more restless and finally, looking up with a troubled face, said merely, 'Mommie, I'm afraid.' "

Wolf, Anna W. M. The Parents' Manual: A Guide to the Emotional Development of Young Children. New York: Simon and Schuster, 1951. (p.163)