Davis, the mother of a gender nonconforming child, explores the boy-girl divide in Tomboy: The Surprising History and Future of Girls Who Dare to Be Different (Hachette Go, May.).

Your 2017 New York Times op-ed—about adults questioning the gender identity of your daughter who dressed like “a boy”—prompted a backlash.

I wrote about a family experience and expressed support of trans rights, but the piece was nuanced and nuanced points are easy to manipulate. When I reached out to my critics, saying, “I’d like to meet you and understand your point better,” I learned that gender is a belief system: different words mean different things to different groups. I couldn’t shepherd my child through these rapidly changing definitions unless I learned this language myself. We’ve gendered too much of childhood, cutting off healthy explorations of identity, activities, colors, and clothing. The more you label boy and girl, the less children explore.

You write that “there’s no such thing as ‘just a tomboy.’ ” What do you mean?

For 150 years, tomboy was a relatively positive term, but that positivity ended at puberty. Girls could have boyhoods as long as they didn’t become “masculine” women. The language is evolving. Stereotypes and gendered terms still exist. I don’t know what the best words are, but I believe in respecting whatever anyone wants to call themselves. Whatever language helps us with that, I hope we find it.

For generations American babies wore white frocks, but the 1920s introduced girl and boy clothing, colors, and toys. What caused this pink-blue split?

Gendering of children’s material worlds coincided with the rise of sexology, psychology, and ideas of how behavior and childhood shaped sexuality. These gender-role uniforms costumed young children so they would know how to be men and women later, and we soon believed wearing them was natural.

Is gender-neutral child rearing the answer?

Some think it’s too passive in the face of pernicious gender stereotypes. “Gender neutral” often means male, but it’s not about limiting your child to things nonthreatening to male children. It’s about actively encouraging participation on both sides of the pink-blue divide: colors, dolls, sports, the entire sphere of possibilities. To be equitable, we cannot make gender the major criterion for decision making regarding their lives.

Have LGBTQ advances made “tomboy” an obsolete notion?

When you call a girl who’s sporty, active, and unconcerned about her appearance a tomboy, you’re saying those things belong to boys. Trans people were often told “you’re not trans, you’re just a tomboy.” But for over 150 years, it created space for girls to transcend boundaries. Real gender freedom means boys, girls, and children who identify as neither are accessing both the pink and blue sides.