The number of children aged 10 and under who have been referred to NHS support services to help deal with transgender feelings has more than quadrupled in the last six years, the Victoria Derbyshire programme has learned. Here is the story of two of the youngest transgender children in the UK - with permission from their parents and with the support of the children's schools.

Lily and Jessica, not their real names, bound into the room full of energy, giggling and chattering away as they carry bags full of toys.

The two friends, six and eight, are clearly delighted to be in each other's company as they empty their stuff on to the floor - dozens of Hello Kitty cuddly toys and Monster High mannequins. Both girls are keen to reveal the names of the dolls (Zoo-Keeper Kitty, Disco Kitty) and which of the toys they admire the most.

So far, so ordinary. A scene replicated up and down the country every time two girls get together for a play date.

Except both these girls were born boys. Within a couple of years, as soon as they could talk in fact, they were preoccupied with anything normally associated with girls - dresses, jewellery, dolls and girls' names.

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Watching these young girls play, there was absolutely nothing to suggest they had been born boys. Lily was dressed in a black T-shirt, a black skirt adorned with pink embroidered flowers and black tights. Jessica was wearing jeans, boots and a pink top.

One had their hair cut in a bob, the other's was shoulder length. They were girls to look at, in the way they dressed, played, and the things they talked about. "Jessica" and "Lily" were the names they had chosen for themselves that day, to protect their identity.

"When did I decide I was definitely a girl? Well my whole life really," Lily says matter-of-factly.

According to their parents, from an early age Lily and Jessica were very aware of gender. They became increasingly unhappy with their gender and were drawn to dresses and toys more typically associated with girls.

And not unhappy in the way a child might be unhappy if you forced them to tidy their bedroom or eat sprouts. Lily and Jessica were becoming uncomfortable and even distressed about being boys.

"If I had to live as a boy I would be really upset," Lily says. "Really upset. But now I'm sort of living as a girl I feel much better." It's a medical condition known as gender dysphoria or gender variance.

Media playback is unsupported on your device Media caption Lily

Before I went to meet them, I confess I was sceptical that children of such a young age could apparently be clear that they had been born in the wrong body.

How could anyone so young be so sure they identified as the opposite sex, wanted to wear girls' clothes, play with dolls and hang out with the other girls in their class? Surely like my own primary school-aged children (both boys) their preferences, likes and dislikes, changed week by week?

But these children seemed adamant. Their parents told me they too had thought it might be a phase, that they'd grow out of it - but if it is a phase, it's one that's lasted several years.

Jessica, whose favourite subjects at school are maths, reading, art and history, explains that when she was a boy, it was "really frustrating for me. It felt like I didn't fit in".

There was a time when she wasn't able to go to the loo at school at all because the boys "thought she was a girl" and didn't want her to use their toilets, and she wasn't allowed to use the girls' loos. Jessica got to the stage where she wasn't drinking any water at school so she could hold out until she got home.

Once a dinner lady thanked her for picking up some cutlery from the floor by saying "good boy", to which Jessica reacted badly and began shouting and screaming. It took five teachers to bring things under control.

Tips from Jessica and Lily's parents

1. Don't panic, you are not alone. Contact Mermaids who can help you get in touch with support networks. Meeting other parents is invaluable.

2. Research! Gires is a great source of information. Watching online videos of trans kids, like "I am Leo", is really helpful.

3. Ask your GP for a referral to the NHS Tavistock Gender Identity Service.

4. Allow your child to express how they feel and dress in whichever gendered clothes they choose to build self-confidence and to discover who they really are.

5. Support, love and accept your child for who they are. And help those around you to understand and accept your child too.

No-one has accurate numbers of how many people experience gender dysphoria in the UK. A survey of 10,000 people by the Equality and Human Rights Commission in 2012 suggested that 1% of the population was transgender. But the truth is no-one really knows because many people never seek help.

The UK's only centre specialising in gender issues in under 18s is the Tavistock and Portman NHS Trust which has clinics in London and Leeds. It says that gender dysphoria in young people is a "complex and rare condition where there is incongruence between the young person's perceived gender and their biological sex".

Over the past six years there's been a four-fold increase in children aged 10 or under being referred to the unit in 2014-15, compared with 2009-10. Of those children, 47 were aged five or younger and two of the children were three years old.

One charity which supports parents with kids who are uncomfortable with their gender is Mermaids. Its head says she's received around 60 calls in the past year from parents of under 10s who think their child might be transgender.

There might be some who would attribute the situation to the parents - that it must be the way they brought their child up, spoiling them rotten, indulging them, or maybe they inadvertently "conditioned" the child in some way because they wanted a girl instead of a boy?

That's not what I found. I found parents who'd gone through mental anguish - who had questioned if they had done anything wrong, and who now appeared to be coping admirably with a very difficult and sensitive situation.

They were bewildered and upset - particularly as both had older boys who were "typical" boys. These were parents who'd never heard of "gender dysphoria" until they'd Googled "should I worry if my son wants to wear a dress?".

Lily's mum Jen explains that she recalls Lily, aged four, then still being treated as a boy, coming into the bedroom as she was putting a dress and necklace on. Lily said: "Wow - can I wear a dress like that when I grow up?" Jen says they thought it was "quite cute" but that he'd grow out of it and "maybe grow up to be gay".

Lily had a couple of "massive" tantrums at around the same age when asked to remove a dressing-up dress at a friend's house. Jen recalled it was a battle and Lily was distressed, but also determined to keep the dress on. She says she realises now that it was probably such a wonderful experience for her to be able to wear a dress that to be asked to take it off and put boys' clothes back on was difficult.

It caused tension with Lily's grandparents. On one outing, her grandmother tried to stop Jen buying her grandson a pink sparkly rucksack, in case it "encouraged him".

Jen explains: "Coming to terms with the fact that your child is probably trans is very hard. We watched a video two years ago. It was an American video of families talking about having transgender children and I thought , 'my gosh, this is what we're facing'."

There wasn't a specific moment when Jen and her husband realised their child was experiencing gender dysphoria - it was something that happened gradually.

"He was three and in a toy shop and he wanted a Barbie doll. Back then I did say, 'that's what girls play with - let's go and look at the trucks and cars'. But he was always drawn towards everything girly. Aged two and three he always wanted dolls, pink glittery things, princess stuff.

"As a parent that's confusing. You do think - how do we deal with this? What do you do in a shoe shop when your boy wants girls' shoes? Back then I was embarrassed and tried to steer her away to buy something else instead."

Jessica's dad and mum Ella split up some years ago. Ella is now in a long-term relationship with another woman, Alexandra, who Jessica calls "step-mum". Ella has considered whether her relationship has contributed to her son wanting to live as girl. Yet she points out she has two older sons, raised in exactly the same way.

"Yes, it did cross our minds. But there is nothing we have done to make this happen. You couldn't put a little boy in a dress if he didn't want to wear it." She then tells me about the relative who accused her of "conditioning" her son, an accusation the couple laugh off as absurd.

Media playback is unsupported on your device Media caption Jessica said she would never change her mind

One of the most difficult times for the family came when an anonymous call was made to the NSPCC to report the pair for "forcing their boy to live as a girl". They were livid, particularly as they thought it came from a member of their family - but the investigation came to nothing.

When Ella realised her child might be transgender, she says she and Alexandra were in "a daze, a stupor" and couldn't believe it. Now they call her by a girl's name, allow her to wear girl's clothes and she even wears a dress to school, because they say it makes her happy and content.

Yet Jessica's dad has been finding it difficult to accept that his son wants to live as a girl. She stays with him every other weekend and until recently he wouldn't allow her to bring skirts and dresses to his home and he would call her by her "boy name". Now he's changed his mind and Jessica says she's much happier now when she visits.

Experts say gender identity issues can be traumatic for a child and their family, particularly when the child reaches puberty. The Tavistock and Portman NHS Trust says in the case of young children, they monitor them over time and "whilst they 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".

Instead their approach involves facilitating counselling and support sessions. Any medical intervention isn't considered until a child approaches puberty, when hormone blockers might be offered.

Blockers delay the physical change of puberty, allowing a young person time to live as a man or woman in the longer-term, after which a patient can consider taking cross-sex hormones at the age of 16, and surgery after 18. The estimated cost of gender reassignment surgery on the NHS is around £10,000.

Why are some people transgender? There isn't a huge amount of research into why. The most recent review of the evidence that is available, carried out by Boston University's School of Medicine earlier this year, points to it being a biological explanation, but suggests more work needs to be done to see if it's down to genes, hormones, or another reason.

Life can be very tough for trans people. According to research published last year by PACE, a mental health charity, 59% of transgender young people said they'd self-harmed, compared with just under 9% of all 16-24 year olds.

It's something Lily and Jessica's parents hope they can protect their girls from, and it was the reason why they and the girls were happy to talk about their situation - raising awareness, they believe, is the only way to combat the stigma, bullying and prejudice many trans people face on a daily basis.

Yet Jessica and Lily are still so young. How can they really know, at such tender ages, that despite being born boys, they really do want to live the rest of their lives as females? The Tavistock and Portman Clinic say it's difficult to predict gender outcome in pre-pubescent children and there's evidence that for many young children experiencing gender dysphoria, those feelings don't persist into adulthood.

I can only go on what Jessica, Lily and their parents told me. When I asked Jessica if she might change her mind in the future and want to live as a boy again, she was adamant she wouldn't - not at 18, 40, 50 or even a 100 she said.

She now goes to school wearing girls' uniform and is delighted that her friends and teachers have accepted her for who she is. Her mum adds that she's "like a typical eight-year-old girl. She's so happy and just smiles and beams. A delight to be around."

Meanwhile, Lily's mum simply wants her daughter to be content, enjoy life, have friends and do well at school - much like the mother of any six-year-old girl.

All names have been changed in this interview. The children, their families and schools gave consent for the interviews to take place. The Tavistock and Portman NHS Trust welcomed the interviews and said it was "encouraging that the BBC interviewed two children who currently identify as being transgender".

For more information and support:

NHS page with general information

Mermaids gives support for children, young people and their families

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

The Gender Trust gives support to the over 18s.

Gender Identity Research & Education Centre

Gendered Intelligencegives support to young people.

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