In any event, boys start to compare the fact that they have penises with other facts they come to recognize, that girls have vulvas rather than penises, that women grow breasts, get pregnant, give birth to babies, and nurse babies at their breasts. As the cognitive categories of present and absent are created, a boy wonders about his own body. Could he lose his penis and look like a girl? Could he have babies and nurse them? Longing, envy, and fear mix with interest and awe.
Neil Altman, Richard Briggs, Jay Frankel, Daniel Gensler, Pasqual Pantone – Relational Child Psychotherapy p.97