Shyness over children's sex education can cause deep distress later.

Wang Wei was a little boy when he asked his mother the question many parents dread to hear: Where do babies come from? The answer he received that day was a lie - but try telling him that.

Students from the No 3 Primary School in Beijing's Huairou district listen to information about sexual health at an exhibition last week in the capital.

Now 15, the Beijing schoolboy still believes he was "found as a baby in a pile of rubbish", explained Wen Fang, director of Xicheng district's Youth Health Center, who talked to Wang when he called for advice on how to sue his "fake parents".

Although extreme, Wen, a therapist for more than 25 years, said the case highlights the taboo that exists about sex education in China.

Not only is the information shortfall causing confusion for teenagers at a delicate stage of physical and emotional development, it is also indirectly behind the soaring abortion rate and the spread of sexually transmitted diseases.

Experts also argue a lack of sexual knowledge is leading to higher divorce rates and a peak in shengnu, "leftover women" unable to find husbands.

"Some (men and women) just don't know how to deal with relationships and how to communicate with partners," said Zhang Meimei, deputy director of the capital's Sexual Health Education Institute.

The country has spent more than 30 years opening up its society and economy, yet the standard of sex education has failed to keep up, with many conservatives fearing that talking about sex will inevitably encourage children to start having intercourse.

Even for those exploring new educational methods, standards are still not in place, while most still carefully avoid the word "sex".

Last year, researchers at Peking University surveyed more than 22,000 youngsters aged 15 to 24 across 25 provinces. Although 22.4 percent admitted losing their virginity, only 4.4 percent were found to have a clear understanding of sexual health.

Roughly half of respondents said they did not use protection the first time and, of the female students who had sex, one-fifth said they have been pregnant, with 5 percent pregnant more than once (90 percent underwent abortions).

As well as the early onset of puberty, health studies show that youngsters are now a high-risk group in terms of HIV and AIDS infection.

"People easily fall over in the darkness," said Chen Shouliang, 80, a retired professor and one of the first to lecture on sex in China. "The more you try to hide (knowledge), the more curious children become."

He complained that most schools and universities "don't even address the basics about sex".