A-1. Youth actually is sexually active 

Third have sex below legal age - Nearly a third of 16 to 24-year-olds lost their virginity below the age of consent, a survey has suggested. news.bbc.co.uk, 2006/08/13

The BBC Radio 1 poll also suggested 43% of young people had had at least five sexual partners with one in five having more than 10. Over half - 57% - claimed to have had a one-night stand.

Teens heavy porn users: study - Michelle Mark - Sun Media & cnews.canoe.ca, February 23, 2007

A groundbreaking study on porn use by 13- and 14-year-old teens shows an alarming number are watching "more times than they can count" and their parents are unaware.

Disturbing Trend: Teens Consenting To Sex Parties - CBS 3, Topix.net, April 02, 2008

CBS station KTVT-TV in Dallas has an exclusive look at the troubling trend of local teenagers taking part in sex parties. One Dallas family wants you to know what happened to them. [...]
"It goes back to being in the in-crowd," she said. "[Kids think] if you want to be popular, this is what I need to do."

For kids, is 10 the new 15? From dating to cell phones, music to make up, behavior shifting earlier - The Associated Press, November 26, 2006

Child development experts say that physical and behavioral changes that would have been typical of teenagers decades ago are now common among "tweens" -- kids ages 8 to 12. Some of them are going on "dates" ...
They struggle to process the images of sex, violence and adult humor, even when their parents try to shield them. And sometimes, he says, parents end up encouraging the behavior by failing to set limits -- in essence, handing over power to their kids.

Doctors' code of silence from parents, to cover up under-age sex - Daniel Martin, Daily Mail, UK, 28th September 2007

Parents will be denied the right to know if their child is having under-age sex under controversial guidelines for doctors unveiled yesterday.
Doctors were told they should not tell parents if children up to three years below the age of consent approach them for contraceptives or an abortion.
There will even be times when parents would not be informed if children under 13 are sexually active.

Boy's family fights sex charges - United Press International, upi.com (US),December 8, 2008

Several teenage girls in Mequon, Wis., say they object to a classmate being criminally prosecuted for allegedly touching them inappropriately. [...]
[...] experts will give their opinion on whether a 13-year-old boy can be sexually aroused by grabbing a girl's buttocks [...]. 
Prosecutors allege the boy several times in 2007 and in June 2008, when he was 13, grabbed the girls' buttocks or their breasts, licked a girl's neck and tickled a girl in the stomach.

Should Sexually Active Minors Have a Right to Privacy? - A Kansas Case Reveals the Dark Side of Mandatory Reporting - Sherry F. Colb, February 8, 2006

[...] In considering whether to require the reporting of teen sex, the first question is always this: What is our view of teenage sex? Many teenagers take the position that if they are old enough to reproduce, then they are old enough to have sex. [...] 
If Tony Teenager knows that going to the doctor will expose him to Department of Social Services intervention, he might decide not to go to the doctor at all. [...]
The privacy rights of teenagers and the hope that fewer of them will have sex prematurely both counsel a far more nuanced approach.

Tangled web - Tom Geoghegan, BBC News Magazine, 9-2-2007

As a European-wide project is launched to examine children's use of online pornography, figures show one in four teenagers with access to the net view porn at least once a month. For some it's an obsession, for others, an adolescent rite of passage.

Fewer U.S. teens have sex; more wear condoms - Jennifer C. Kerr, Associated Press, July 13, 2007

Fewer high school students are having sex these days, and more are using condoms. The teen birth rate has hit a record low. [...]
In 2005, 47 percent of high school students -- 6.7 million -- reported having had sexual intercourse, down from 54 percent in 1991. The rate of those who reported having had sex has remained the same since 2003. 
Thirty-four percent of the students reported having had sex during a three-month period in 2005. Of those, 63 percent -- about 3 million -- used condoms. That's up from 46 percent in 1991. [...]
Education campaigns that started years ago are having a significant effect [...].