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.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?