Louis Theroux travels to San Francisco, where a group of pioneering medical professionals are helping children who say they were born in the wrong body to transition from boy to girl or girl to boy at ever-younger ages. At the Child And Adolescent Gender Center at UCSF Hospital Louis meets children who have been diagnosed with gender dysphoria. Louis is told that children as young as three can show signs of rejecting the gender they were assigned at birth, leaving parents with a difficult dilemma - do they start transitioning a child who is still developing their own identity, or do they wait and risk making the change once their body has gone through the transformations of puberty? It is a decision that can be the start of a complex series of medical interventions, from puberty blockers to hormone replacement therapy and eventually gender reassignment surgery. Louis spends time with children and their families as they negotiate their way along this life changing and emotional journey.