Leave your son alone. If he has a strong desire to dress in womans clothes, he will do it now and then for the rest of his life, whatever you say or do. If he is doing it for curiosity, he will overcome it faster if you do not comment on it.
Transgender behavior is more common than most people realize and usually causes no big problems unless other people get overly concerned about it. It does not mean that a person is homosexual, many people who sometimes behave in transgender ways are at the same time heterosexual and have no interest in sex with their own gender.
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