I feel much better as a girl'
Victoria Derbyshire has been speaking to two of the youngest transgender children in the UK - with permission from their parents and with the support of the children's schools. Medical experts were also consulted.
"Lily", six, was born a boy, but is now living as a girl. She told Victoria Derbyshire what it was like to feel like she had been born in the wrong body. It is a medical condition known as gender dysphoria or gender variance.
"When did I decide I was definitely a girl? Well my whole life really," Lily said.
"If I had to live as a boy I would be really upset. Really upset. But now I'm sort of living as a girl I feel much better."
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