Why do you think Bruno's mother fails to tell her son the exact nature of his father's Job?

Bruno's mother likely fails to explain her husband's job to him because she wants to protect him from the harsh realities of their situation. She may also be conflicted about the morality of her husband's work and fears that revealing the truth would expose Bruno to the disturbing implications of their lives. Additionally, as a mother, she might struggle with her own feelings of denial and hope to shield her son from the darkness surrounding them.