It's the first question that's asked, before we're even born, "is it a boy or a girl?", but for an increasing number of children the answer isn't straightforward. The first film in this series follows two children, Ash and Matt, and their mothers, as they attend the Tavistock's Gender Identity Development Service, and wrestle with life-changing decisions.

The second episode follows three children who attend Gloucester House, the Tavi's day unit. This unique NHS-run primary and early secondary school is for children with complex emotional, social and behavioural problems and has a specialist team of teachers, mental health nurses, therapists and support workers who work intensively with its 18 students, many of whom have been excluded from mainstream schools.

Self-harm and suicide are major public health problems for teenagers. Although boys are by no means immune, one in three UK teenage girls is now said to report symptoms of anxiety or depression. Episode three tells the stories of two teenage girls – Demi and Maisie – who have repeatedly self-harmed, and shows the support they receive from Tavistock clinicians.