Ms. Prince, the author of “Tomboy,” spoke with annoyance about late 1990s movies like “Clueless” and “She’s All That,” in which “there’s this tomboyish character that gets a makeover and strictly conforms to gender roles and becomes more popular,” she said. “That was a really annoying narrative to me.”

But some two decades later, Ingrid Bowman, 43, an engineer who lives in Raleigh, N.C., is in no rush to nudge her 11-year-old daughter, Alexandra, who has worn her older brother’s clothes and hung out with boys her whole life, into rustling taffeta frocks — even if other adults are.

“They’d drop comments like, ‘You know we’re having a dress event, would Alexandra ever wear a dress?’ ” Ms. Bowman said. “I’d say, ‘I don’t know, are you going to wear a dress? She’ll wear whatever she wants to wear. She looks awesome.’ ”

Christine, a sociologist in the Glen Park neighborhood of San Francisco, has identical twin daughters, Charlotte and Stella, who at age 8 have passed the princess phase. At least Charlotte, a former champion of tiaras who now prefers leggings and athletic gear, has; Stella, who now wears short hair and boxer briefs from the boy’s department, never had one.

“People would call her a tomboy or assume she’s a boy. I don’t correct them — it’s not that important,” said Christine, also honoring her girls’ request that their last name not be used, and who with her husband, Matt, is also raising two sons, Jude, 10, and Jackson, 13. “We don’t use ‘tomboy’ in our family. It suggests there’s a regular way to be a girl, and this is another way to be a girl. I’m just listening and letting Stella say who she is.”

Angelina Jolie and Brad Pitt also appear to be letting their daughter Shiloh say who she is: reportedly someone named “John,” who judging from paparazzi photos regularly wears boys’ clothes.