Symbolism, Imagery, Allegory
Edward isn't the tough, manly son that his parents want him to be. Instead of playing rough, stereotypically boyish games, Edward likes playing with his sister Victoria's doll.
At first Clive tries to dismiss Edward's preference for the doll by assuming that Edward is just minding the doll for his sister. But then Edward keeps showering love on the adorable dolly, and Clive and Betty kinda lose it. When his mother catches him playing with Victoria's doll a second time, she says, "You must never let the boys at school know you like dolls. Never, never" (1.3.66). Even Joshua tears the doll in an attempt to destroy Edward's "feminine" attachment to it.
No matter what his parents do, Edward can't change who he is. He fantasizes about having sex with Harry Bagley instead of with women, and he shows little interest in making his school's cricket team. Edward can't change who he is, and the doll continues to symbolize his nurturing, gentle, feminine side.
Edward's gentle side comes out in Act 2, when we see him taking the "feminine," submissive role in his relationship with his lover Gerry. The doll isn't just a passing phase: it's symbolic of Edward's true nature and foreshadows the man he will grow up to be.