NEW YORK (AP) -- "Growing Up Trans" explores the transgender phenomenon as younger people than ever (and their parents) now experience it: a frontier of possibilities and unknowns, and a minefield of high-stakes choices for these youngsters as they also navigate the changes adolescence brings.

This image released by PBS shows transgender teen Ariel in "Growing Up Trans," airing on PBS on Tuesday, June 30, 2015. (Frontline/PBS via AP)

Airing on the "Frontline" documentary series (Tuesday on PBS; check local listings), it begins with 9-year-old Lia (formerly Liam) Hegarty, who says she transitioned when she was about 7 and now is "almost completely female."

Ticking off the steps with each finger, she says, "I've changed my name, my clothes, my room and my pronouns. And that's really all you need." Except for the fifth step, she adds, looking ahead as she presents her thumb: "Surgery and medicine."

But through it all looms doubt and risk.

"We're asking families to take some leaps of faith," says Dr. Robert Garofalo of Lurie Children's Hospital in Chicago, who cites vexing uncertainties from as-yet-unproven drugs and procedures.

"How realistic is it to believe that a 14-, 15-, or 16-year-old has the capacity to make that kind of decision for him or herself? But at the same time, to deny them -- that's tough," he says. "This is tough stuff."

Ariel (formerly Ian), 13, wants to have children someday, but not from sperm that could be stored from the male body she was born with. Yet she grieves that the girl she is transitioning into can never carry a child.

Otherwise, she is pleased with the path she has chosen, and considers her puberty-blocking drugs "my lifesaver. Me turning into a man is just probably the most horrifying thing ever."

Though some adults may face a steep learning curve about transgenderism, the younger generation -- whether trans or not -- seems to be dealing with it. That was what led filmmakers Miri Navasky and Karen O'Connor to choose kids as their focus.

"We thought going inside a world that appears more accepting, and, through that lens, trying to tease out all the complications, might allow us to learn things that hadn't been shown before," says O'Connor.

Indeed, they have journeyed back to square one for this new wave of subjects, capturing them much earlier in life than widely recognized trans trailblazers like Chaz Bono and Caitlyn Jenner.

The veteran "Frontline" filmmaking team spent more than a year on "Growing Up Trans," which left them marveling at how their young subjects "had processed an enormous amount about themselves and how they function in the world," says Navasky. "They were so in touch with themselves."

Meanwhile, the filmmakers realized they were telling a larger story than that of transgender people.

"It also becomes about parenting," says O'Connor. "What do we do when faced with our child's pain and anguish, in whatever form, and when faced with so many choices and medical unknowns?"

Alex's parents feel burdened as they weigh the unknown consequences of puberty blockers meant to halt his menstruation. At 13, Alex (formerly Karen) dreams of a flat chest, a deep voice and an Adam's apple. He loves to skateboard with a couple of guys who, in a boys-will-be-boys display of male bonding, share how they "show him the ropes" of being a dude -- like directing him to burp out loud ("don't try to hold it in").

When his parents meet with Alex's doctor to sign consent forms for his testosterone regimen, they are braced for the necessary leap of faith.

"When you see a child suffer and struggle the way we have seen Alex struggle," his mother sums up, "we don't have a choice."

Not every case is so communal. John's father refuses to accept his son's chosen gender identity, explaining he feels "robbed -- my daughter's gone" and voicing disbelief that life as a male is "the path that God has planned for her."

Then we meet 18-year-old Lia Hodson, who has run the gantlet of puberty blockers and cross-sex hormones and now is ready for the final step. But her so-called bottom surgery is much ado about next-to-nothing, she says cheerfully: "I'm just a girl. I'm just myself. I don't really like making it a big deal."

For her and the others the film profiles, it's too soon to declare any happily-ever-after outcomes, and "Growing Up Trans" doesn't. But its storytelling speaks of hope for what emerges as a breakthrough quest for being true to oneself.

"We aren't minimizing stories of real anguish out there," says O'Connor. "But wherever we went, we realized we're on the verge of a generational shift." Their film sheds light on why.

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