I imagine that if I had a son, I would probably buy all of his clothes for him... If what he wanted to wear were "girl" clothes, including the "foundation garments" to make them look appropriate - why would that be any different?
I'm guessing the question comes from more of a place of sexuality than of transgender identity.
Even if it were about sex, it would still be a non-issue for me - I would make sure my kids had condoms galore too, regardless of the clothes they were to wear.
