This paper addresses the issue of whose genitalia is involved in the dissolution of the castration complex in boys. Freud and his followers suggested several different possibilities which are elaborated herein and these possible models are discussed from the perspective of psychological research regarding children's awareness of genital differences. The reviewed data show that contrary to Freudian theory, preschool children are not generally aware of genital differences. However, preschoolers with younger siblings, primarily opposite gender ones, evidence greater understanding of genital differences, as Freud suggested. The discussion emphasizes the importance of children's family constellation in the development of their gender identity.