Under a controversial National Health Service (NHS) scheme, children as young as 13 are being sent sex advice by text message.
They are being encouraged to send in questions about losing their virginity, where to get the morning-after pill and how to get tested for infections.
Within minutes they receive a detailed reply from a specially trained advisor, paid for by councils and local health trusts.
The scheme is targeted towards those aged 13 to 25 to increase awareness about issues such as contraception and teenage pregnancy.
But those who text in are not asked their age - so there are fears that much younger children could be receiving detailed sexual advice.
The advisors are also texting girls that it is 'safe' to take the morning-after pill more than once, even though there are concerns that frequent use encourages the risk of sexually transmitted infections.
The service is funded by health trusts and councils and is being run in the London boroughs of Enfield, Kensington and Chelsea and Hammersmith and Fulham.
Youngsters are not charged and they can send texts any day of the week, between the hours of 8am and 2am. They receive a response from one of 100 health advisors who work in shifts from a call centre in London.
The scheme was introduced last year amid concerns that teenagers were having sex without being fully aware of the consequences.
But campaigners warn that the text service - funded by taxpayers - is simply encouraging promiscuity among underage youngsters.
"Not only does it undermine parents by presenting itself as an authoritative source of advice on sex, relationships and sexual health, but it also fails to respect the age of consent by offering a service to children under 16," the Daily Mail quoted Norman Wells, director of Family and Youth Concern, as saying.
"The information provided is not even accurate. The website fails to tell visitors that condoms provide much less protection against sexually transmitted infections than they do against pregnancy, and says nothing about the health benefits of keeping sex within a lifelong, mutually faithful relationship with an uninfected partner," Wells added.
Around 500 texts are sent to the service, called txtm8, every month and the number are advertised on council websites and social networking sites.