In 2004, Ms Sheena Jebal counselled a sexually active 10-year-old girl.

'Back then, she didn't know what she was doing. But now, youth as young as 10 to 12, they know what they are doing,' said Ms Sheena, a counsellor at Nulife Care and Counselling Services in Ang Mo Kio.

She is not alone in detecting a trend of pre-teens engaging in sex. The numbers are still very small, say counsellors, but the trend appears to be rising.

What is striking is how the children were clued in about sex through what they saw online. Interestingly, too, the cases involve children of both genders and not the more common young girl-adult male combination.

Dr Carol Balhetchet, director of youth services at the Singapore Children's Society, has seen three cases of sexually active children aged between 11 and 13 this year.

Such cases were rare before, she said, noting that the trend became more visible last year.

The issue was highlighted last week when the Community Court heard the case of an 11-year-old girl who had sex with a 16-year-old boy last year.

They met after chatting on the Internet. She told him that she was 12 and in Primary 6, and they split up after two weeks as the girl felt they had begun to drift apart.

The girl, now 13, is believed to have had sex with a second boyfriend, who was then 16. The first boy, now 17, has been put on probation.

Sex with a minor under 14 is punishable with a jail term which may extend to 20 years, along with a fine or caning. The penalty for having sex with a girl under 16 is up to five years' jail and a fine of up to $10,000.

Associate Professor Munidasa Winslow, a specialist in psychiatry at Raffles Hospital, estimates there has been a 50 per cent increase over the last 20 years in the number of patients who report becoming sexually active at 14 and below.

Two years ago, a lifestyle survey he did of students between Secondary 1 and 3 showed that about 60 out of 1,000 students were having sex.

Why are they starting so young?

Said Dr Balhetchet: 'A lot of it has got to do with youths' exposure to various media that suggest that expressing sexuality is something they should be comfortable with.

'Combined with a lack of adult supervision and boredom, one thing will lead to another.'

Said Prof Winslow: 'Teenagers find a thrill in obtaining and watching pornography and with the Internet, they are far more sexualised now.'

Indeed, Ms Sheena now sees many young girls besotted with the idea of being in love because of influences from the mass media and peer pressure.

'They will just copy what they see others do, like holding hands or kissing in public,' she said.

Of the three cases that Dr Balhetchet saw this year, one involved two 12-year-olds - a boy and a girl - who had visited a pornography website.

She got to know the couple after the girl was placed on a beyond parental control order. The girl's mother also made a police report against the boy.

The girl was the oldest of three children and was always out of the house. She had sex with the boy and others too.

Said Dr Balhetchet: 'They just looked like normal 12-year-olds. Previously, the girl might be more well-endowed or the boy might be bigger, but it isn't the case any more.'

While children physically mature only upon puberty - on average at age 12 for girls and between 13 and 14 for boys - children today may exhibit sexual behaviour in early childhood.

'There are extremes of children between four and six years old who exhibit sex play because they have been exposed to media which glamorises sex,' said Dr Cheng Tai Kin, a paediatrician at Kinder Clinic in East Shore Hospital.

'This kind of socialisation is becoming more common, so sex play, which normally emerges at a more physically and emotionally mature age, can occur in very young children.'

Sex play involves children exhibiting sexual behaviour or pretending to have sex.

It is also becoming more common for younger teenagers to engage in sex, he said. Two years ago, he saw a case of a pregnant 13-year-old. 'She was just a normal child,' he said.

Experts say sexual encounters tend to take place in the home when the youngsters are alone.

Among two youth close in age, sex is usually the result of boredom or curiosity. It often occurs among children with family problems or latch-key kids, said Dr Winslow.

Dr Balhetchet noted that in cases where one teen is much older than the other, there may be some mental or emotional coercion.

Experts said pre-teens and teens may develop sexually transmitted infections or become pregnant as they are less likely to use protection.

They may also start believing that they are grown-up and independent and may even run away from home, said Ms Sheena.

Dr Warren Lee, a paediatric endocrinologist in private practice and a senior consultant at KK Women's and Children's Hospital, said children these days tend to develop sexually before they are emotionally mature.

Ultimately, said experts, the responsibility must lie with parents.

Said Dr Lee: 'It is up to parents to encourage responsible development of the mind and soul even as children are physically developing. If a child is physically 12, parents should ensure that he is also 12 years old emotionally.'

Added Ms Sheena: 'Children are exposed to so many elements like the media and school, there is no way to avoid it. Parents can help through supervision, by being involved in their lives and knowing what they are up to.'

This article was first published in The Sunday Times on Dec 14, 2008.