The world of The Turn of the Screw is dominated by women, whose lives in turn are dominated by men, whether they know it or not. Gender plays a huge role in the development of the rather warped network of relationships that James crafts here; though sexuality is never, ever openly discussed, you can be sure that James meant for his readers to ponder the various permutations of desire and power that arise out of gender struggles. Part of the difficulty is the question of how much a woman can truly control a man – or even a male child. Even in our more equitable era, it's easy to see the issues that James gets at here.
James emphasizes the simultaneously ridiculous and eerie precocity of Miles's character to depict him as a man in a house full of women.
The idea of Miles's possession by the spirits is more menacing than Flora's because he is male, and therefore ultimately more capable of harm.