Little Fayoumis was surprised, and said that it looked like a girl. I told him that yeah, it was kind of hard to tell if it was a guy or a girl unless you already knew, and that the word for it when you can't tell if it's a guy or a girl is "androgynous".
"He's really androgynous," Little Fayoumis declared, murdering the word, but grasping it utterly.
That really is the way to slip in those nice vocabulary words -- in context, when the kid is clearly searching for the right word that they don't know yet, and are happy when a grown-up tells them a word that fits what they mean exactly. (And it also weirds me that so much of the thinking is done with these words -- they make elaborate constructs possible to store and modify, but unless one's accustomed to being a wordsmith (writer of me?), one can't say anything new compactly.