In Hong Kong, children as young as 11 are having sex.
And researchers say more and more young people are becoming involved in sex crimes, Hong Kong's The Standard reported on Friday.
The report said that the Evangelical Lutheran Church of Hong Kong had studied 30 cases of underage sex criminals who were referred to the church by police teams from New Territories East.
The study, which focused on four districts, was carried out from April last year to March this year.
The report said that the 30 offenders, all aged below 18, had committed sex crimes.
The age of teenagers committing sex crimes dropped from between 15 and 17 in 2009-2010 to between 13 and 15 in 2012-2013, the church study showed. Of the offenders, two were aged 16, three were 15 and five were 13.
The youngest criminals this year were three boys aged 11. They were involved in indecent assault and sexual harassment.
"It was the first time in our four years of study that we have come across sex criminals as young as 11, and we had three of them," said Mr Keswick Chuk Wing-hung, director of youth services at the church.
The study also showed that in the past four years, 92 per cent of the underaged offenders and their victims were lovers, classmates or friends. And in some cases, the sex acts were by mutual agreement.
Mr Chuk said the use of social networks had made finding sex partners easier.
"They begin by making friends and as a result they become less vigilant," he said.
Many teenagers were not clear about the laws and easily fell victims to sex crimes.
"That is why in many cases the criminals and the victims knew each other."
Mr Chuk said the aim of the study was to help youngsters to prevent them from repeating their crimes.
"The earlier we become involved in their situations, the easier it will be to prevent them from hurting others," he said.
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