'It is completely inappropriate for such material to be on the CBBC website and I shall be writing to BBC bosses to demand they take it down as soon as possible.'
Former Culture Secretary Maria Miller voiced her concerns over the BBC tackling the subject in 'an age-appropriate way', saying such issues should be raised 'where children can have support from parents'.
And Tory MP Julian Brazier said: 'This programme is very disappointing and inappropriate. Children are very impressionable and this is going to confuse and worry them.'
Family campaigner Norman Wells said: 'It is irresponsible of the BBC to introduce impressionable children as young as six to the idea that they can choose to be something other than their biological sex.'
Just A Girl is the fictional video diary of a child who calls herself 'Amy' and dresses as a girl. It is hosted on the CBBC website, aimed at children aged between six and 12.
In the half-hour programme, Amy - played by an actress - reveals she was born a boy called Ben but has already started using puberty-halting drugs.
Such hypothalamic blockers provoked a furore two years ago when The Mail on Sunday revealed an NHS clinic was willing to give them to children as young as nine.
Critics cited research claiming that most teenagers confused about their gender never go through with surgery, with many realising they are gay. The BBC row comes amid growing controversy over gender issues, fuelled by a number of high-profile cases. In one, a Christian couple were threatened with having their 14-year-old daughter taken away because they oppose her plans to become a boy.
In another, a seven-year-old boy was ordered to be removed from his mother's care as 'she was raising him as female', causing him 'a great deal of emotional harm'.
In Just A Girl, Amy says: 'When I was born, Mum said Dad was so pleased that he had a boy to take to the football. But Mum knew I was different. She realised early on that I was born in the wrong body.'
She adds: 'My Mum supported me when I did a PowerPoint presentation to my class about transitioning and that I wasn't going to come to school in boys' clothes any more, but girls' clothes. I wasn't Ben, I was Amy.'
Later Amy is shown telling a friend, Josh - a boy who wants to be recognised as a girl - that she is on hormone blockers, saying it took 'ages' to get them after 'loads of tests and talks at the clinic'. 'Once they realised I was trans for real, [I] got them,' she says. In another entry, Amy tells viewers she has developed a crush on a boy called Liam, but confides: 'Liam thinks I'm just a girl, but I'm not. I'm trans. And what's he going to say if he finds out? Stop being my friend? Why? I'm still me, aren't I?'
Child psychotherapist Dr Dilys Daws said the programme could confuse children. She said that, while it was natural for youngsters to wonder what it would be like to be the opposite sex, the BBC was irresponsible to feature the 'extreme' step of gender change for six-year-olds because they were too young to grapple with such issues.
The programme generated hundreds of comments on Mumsnet.
One mother, who said her seven-year-old had watched the show, asked: 'Am I being unreasonable to think this is an inappropriate topic for a young age group?'
Another replied: 'Don't think this is remotely suitable for a seven-year-old. To start suggesting that children can be transgender when they're far too young to actually have a gender is reckless and damaging. A small boy who is told that he can become a girl may take this as meaning that sex changes are possible, that sometime in the future he'll wake up with a girl's body.'
Another user added: 'I don't think hormone therapy should be normalised any more than 12-year-olds drinking or doing recreational drugs should be normalised.'
Other critics slammed the BBC. Mr Wells, director of the Family Education Trust, said: 'The more we promote the idea that a boy can be born into a girl's body and a girl can be born into a boy's body, and that drugs and surgery can put things right, the more children will become utterly confused. Respecting and preserving a child's birth sex should be seen as a child protection issue.'
But some parents on Mumsnet were more positive. One wrote: 'I don't believe there is "too young" for stuff like this. The earlier you teach your children that everyone is different and that nobody is "normal" the better.'
Dr Polly Carmichael, a clinical psychologist specialising in transgender children, said: 'Raising awareness of these issues is the best way to challenge stigma and discrimination associated with identity issues. Programmes like Just A Girl can contribute to a healthy and informed public discussion.'
The BBC said: 'Just A Girl is about a fictional transgender character trying to make sense of the world, deal with bullying and work out how to keep her friends, which are universal themes that many children relate to, and which has had a positive response from our audience.
'CBBC aims to reflect true life, providing content that mirrors the lives of as many UK children as possible.'
