El sexo sentido (2014)

Between the ages of two and three, children already know which gender they belong to. One in 10,000 males and one in 40,000 females feel the opposite gender to the one they were assigned at birth. The first signs of transsexuality can appear very early. The families of all the protagonists in the documentary agree that their children have, almost from the moment they began to speak, expressed with surprising insistence and firmness that they belonged to the sex opposite to that of their genitalia.