Media playback is unsupported on your device Media caption Jason says he could not carry on living as a girl any longer

Ten-year-old Jason is one of the youngest transgender children in the UK to receive medical treatment to pause their puberty. He tells the Victoria Derbyshire programme what it is like to grow up feeling like you are in the wrong body.

Jason always knew he was not happy growing up as a girl.

He did not feel the same as other children and actually felt like a boy trapped in a girl's body.

One Christmas, he even asked for a magic potion that would turn his body into a boy's.

"Being a girl felt horrible," he says. "Pretty much every day I came home from school crying, because I didn't know how to explain it."

So in April this year, with the help and support of parents and teachers, he began living as a boy called Jason.

Image caption Jason says his friends and family have all accepted that he felt like he is in the wrong body

The Victoria Derbyshire programme has learned that 120 children who identify as being transgender have had NHS treatment to pause their puberty over the last five years.

For his treatment, Jason began having monthly injections called hormone blockers, which effectively halt the progress of puberty - but only temporarily.

His mother Leanne says it was "upsetting to see your child upset", as hers frequently was, because they were uncomfortable in their body.

"We didn't know if it was a phase, whether it was a gay tendency thing, that he was acting more boyish than other girls. But as he got more upset, I knew we had to do something."

Leanne also said that when Jason was three or four, he refused to wear girls' clothes. After about a year his parents gave in and allowed him to wear whatever he wanted. At the age of five or six, he began saying he was not happy in his own skin.

The situation came to a head last year when a teacher saw how distraught he became during a lesson which required some simple self-analysis and mentioned to Leanne that gender issues could be the cause of his distress.

And earlier this year Jason - who was still living as a girl - watched a documentary made for CBBC called "I am Leo" about a 13-year-old, who had been born a girl but felt like they were a boy.

Image caption Leanne says she and her husband paid for private hormone treatment because Jason was so unhappy

Jason says now that watching the programme felt "amazing, a relief", because it made him realise he was not the only person in the world who felt like he did.

He was getting upset, because at the age of nine, his body was already showing signs of becoming more like a woman's, as puberty beckoned quite early.

The family had to wait 15 months to see Child and Adolescent Mental Health Services, which offer assessment and treatment when children and young people have emotional, behavioural or mental health difficulties.

Image caption Jason says he came home from school every day in tears

After that, they faced a further lengthy wait for an appointment at the Tavistock Centre, the NHS's only gender identity clinic for under-18s.

So instead of waiting, Leanne took her child to see a private doctor to begin a monthly course of temporary hormone blockers, at a cost of £100 each month.

The Welsh Government has told the programme it is "working closely with the NHS to reduce waiting times and have included funding in the draft budget for 2017-18 to improve gender identity services for people in Wales".

When Jason is older, he can choose to take cross-sex hormones which are permanent and mean the person goes through the puberty of the gender with which they identify.

Gender identity support for children and young people

1,419 children and young people have been referred to the Tavistock Centre gender identity service in the last year. Of these, 167 were children aged 10 or under

120 children aged under 15 were prescribed hypothalamic hormone blockers from Tavistock between 2011 and 2016. These prescriptions rose from nine in 2011-12 to 43 in 2015-16

So far, three children and young people who started on blockers have decided to stop taking them

24 young people went on to receive cross-sex hormones from the Tavistock around the age of 16

Source: Tavistock and Portman NHS Foundation Trust

Jason says this treatment is "amazing", even though it means he has to have regular injections, of which he is usually terrified.

"If I was to carry on living as a girl, I don't think I could do it. I probably wouldn't come out of my room."

Leanne says she is sure this treatment is the best course of action for her child.

"We've seen this from an early age and he's not come out of it. He's so clear and concise about what he wants.

"We've told him that if he changes his mind he can talk to us, he can always come off the hormone blockers. By the time he's 13 or 14, old enough to take the cross-sex hormones, then he'll definitely know."

Image caption His mother Leanne says Jason disliked wearing girls' clothes from an early age

Cross-sex hormones are only available on the NHS for young people aged around 16 or older, so Leanne would again seek private treatment, if that treatment is what Jason wants.

"It's a massive decision for a parent to take, but it's not something we'd go into lightly," she says. "It's hard for another parent or someone looking in to understand that they are trapped in the wrong body.

"He's so keen and eager to become a boy. He has even discussed further surgeries later on down the line. That's how adamant he is."

Jason has a five-year-old brother who he says has totally embraced the change in his sibling and "hasn't really made a mistake" since his sister became his brother. He also corrects others if they use the wrong name or pronoun when referring to Jason.

Jason is now far happier as a boy. He has a busy life, lots of friends, and is football mad. He would like to become a footballer and play for Manchester United.

"He hasn't changed as a person," says Leanne. "He's still got the same likes and dislikes. It's just that he's a boy."

Jason and his family do not want to hide who they are, but the BBC is not showing their faces to protect him from future online comments which may have a negative effect on him.

Watch the Victoria Derbyshire programme on weekdays between 09:00 and 11:00 on BBC Two and the BBC News Channel.

For more information and support:

NHS page with general information

Tavistock Centre - the only NHS gender identity centre for under-18s.

Mermaids gives support for children, young people and their families

Gendered Intelligence gives support to young people

The Gender Trust gives support to the over-18s

Gender Identity Research & Education Centre