Children as young as three have been referred to the NHS because of transgender feelings.
Two three-year-olds and 47 kids aged five or under were seen at a specialist clinic as the number of child transgender referrals more than quadrupled in five years.
The Tavistock and Portman NHS Trust said the number of under 11s referred to the unit has risen from 19 in 2009-10 to 77 in 2014-15.
Parents said they had sought help after children became deeply distressed about their gender.
Two children, Lily, six, and eight-year-old Jessica - not their real names - were born boys but became unhappy with their gender from an early age, according to their parents.
Jessica said there was a time when she was unable to go to the toilet at school because they boys 'thought she was a girl' while she was not allowed to use the girls' toilets.
The child got to the stage where she stopped drinking water at school to try to avoid the trauma.
In another incident, it took five teachers to calm her down after a dinner lady thanked her for picking up some cutlery by saying 'good boy'.
The child told the BBC's Victoria Derbyshire programme: "I really didn't want to be a boy. It was really frustrating for me. It feels like I'm in the wrong body."
Jessica's mother Ella – also not her real name – said she had been accused by a relative of "conditioning" her child.
An anonymous call was made to the NSPCC claiming Jessica's parents were "forcing their boy to live as a girl".
Her mother split up with Jessica's father some years ago and is now in a long-term relationship with a woman.
Ella said she had considered whether her relationship had contributed to her son's feelings, but points out she has two older sons raised the same way.
"There is nothing we have done to make this happen," she said.
"You couldn't put a little boy in a dress if he didn't want to wear it."
Jessica stays with her father every other weekend, who has found it difficult to accept that his son wants to live as a girl, and until recently wouldn't allow her to bring skirts and dresses to his home.
The Trust said that when young children were referred to them, they were monitored closely, and given counselling and support sessions.
A spokesman said that while such cases 'may fulfil the criteria for a gender dysphoria diagnosis, we wouldn't consider it generally helpful to make a formal diagnosis in very young children'.
When children are approaching puberty, they may be offered hormone blockers, which delay physical changes, allowing a young person time to live as a man or woman in the longer-term.
Although the gender treatment is reversible, concerns have been expressed about possible long-term effects on brain development, bone growth and fertility.
From the age of 16, patients can be offered cross-sex hormones, and gender reassignment surgery after 18, at an estimated cost to the NHS of around £10,000.
A spokesman for the Trust said: "It is probably fair to say that young people are increasingly interested in exploring gender.
"There is not one straightforward explanation for the increase in referrals, but it's important to note that gender expression is diversifying, which makes it all the more important that young people have the opportunity to explore and develop their own path with the support of specialist services."
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