Children are twice as likely to have internet access in their bedroom as a television (source: GfK, eight to 15-year-olds) and the internet is taking a leading role in campaigns targeted at young people.
The most forward-thinking brands are creating bespoke content for websites that reach the highest concentration of children under 15 - such as Stardoll, Yoville, Habbo and Bebo - and driving interaction with these platforms.
Duncan McCrum, head of digital at Viacom Brand Solutions, says competitions are the key to engaging children: "Entering competitions to win prizes is one of the biggest attractions for kids, and involving celebrities also helps."
McCrum adds that children's online use has increased just 2% year on year, so the right strategy should be "less about increasing audiences and more about increasing the number of tools and methods of engaging".
"Children don't like Twitter or Facebook," he explains. "They want space to stamp their identity on things and be creative." He adds that although kids are "far more trusting" about advertising than adults, it is crucial to ensure campaigns are clever.
John V Willshire, head of innovation at PHD, says: "It's not just about slapping banners and buttons all over a site; you must create something in tune with how people are using that site, so they will get into it and share the experience."
Advertisers are starting to move beyond basic branded content and are seamlessly incorporating their products into children's websites. That might involve dressing dolls on Stardoll, earning currency to use on [swapping site] SwapitShop or [virtual world] Bin Weevils or caring for a virtual pet on the Boomerang TV site.
Effective and engaging online campaigns (see case studies) require collaboration between client, publisher, creative and media agencies, and applying learnings from previous activity.
Chris Seth, executive vice-president of international advertising and general manager at Stardoll Network, says: "The idea-generation process relies on audience and consumer insight. We are able to drop into our sites, look at what people are doing and use some of that insight."
Older children looking for greater levels of self-expression enjoy more grown-up sites, such as AOL's jsyk.com - standing for "just so you know" - a news, celebrity and technology site for nine to 15-year-olds that launched in October.
But a great deal of fine-tuning is still required. Emma Ellis, digital research manager at Media Contacts, thinks advertisers are "playing catch-up". She says: "Social media sites have become the fabric of children's everyday worlds and advertisers have suddenly realised they should be following this audience."
With two out of three 12 to 15-year-olds having a social networking profile, advertisers cannot afford to be slow to jump on board.
Piczo: Teaching teenagers to keep their avatars healthy
Brand: Teen Life Check
Client: Department of Health
Media agency: I-Level
Lead planner: Kirsten Nielsen
The Teen Life Check website was created by the Department of Health as part of the NHS drive to encourage 12 to 15-year-olds to lead a healthier lifestyle.
Aimed at teenagers in the C2DE demographic, the site aimed to reach youngsters at a crucial stage in their lives: as they start to make their own choices about their diet and exercise habits. The client gave I-Level the brief to generate traffic and, ultimately, drive users to complete the NHS Teen Life Check survey.
The Department of Health teamed up with social networking site Piczo, which was logged on to from home by 39,000 children aged 12 to 17 in September. I-Level created an NHS Teen Life Check hub within the site, where users could download Tamagotchi-style avatars. These were digital versions of the teenage users that needed constant looking after, or they would get ill and "die".
Content was updated regularly and users encouraged to take part in quizzes and polls relating to their lifestyle. The teenagers had to keep their avatar healthy by feeding it well and giving it virtual exercise.
If the virtual creature became overweight and out of breath, the planning team hoped the youngsters would make the connection with their own health.
The team created a further incentive by awarding prizes at the end of the campaign to those users with the healthiest avatar. Everything on the Piczo hub linked back to users' profile pages, so the campaign became a talking point.
Kirsten Nielsen, I-Level's account director for the Department of Health, says the participatory element was critical to the campaign: "If we had just put the surveys up there and hoped for the best, we ran the risk of being ignored."
Since the campaign went live in July, 15,440 youngsters have visited the hub and almost 1,000 avatars have been created. However, I-Level is focusing on the strength of the campaign's word-of-mouth element.
Nielsen adds: "On paper, this tough audience is put off by the message, but the fact that they are forwarding it to their friends is testament that we did it in the right space. We are confident we used the right tactic and the right voice."
Stardoll: Nickelodeon follows fashion
Brand: True Jackson
Media agency: UM
Lead planner: Natasha Lekka
When Nickelodeon launched True Jackson on UK television, the company set out to create an ad campaign that reflected the show's content.
Billed as an Ugly Betty for kids, the fashion-oriented series was a perfect fit with Stardoll, the website for 11 to 16-year-olds about fame and fashion. Nickelodeon's media agency, UM, had enjoyed previous success with integrated social placements on Stardoll and knew the site was a perfect fit with the show.
The site works by allowing users to dress up virtual versions of themselves and each other. For Nickelodeon's promotion, the planning team put a doll-like version of True Jackson's main character, Keke Palmer, on the site and users could dress her in a range of outfits and share their handiwork with their online friends.
Participants could also send each other virtual gifts and visit Palmer's branded page. The Stardoll Cinema showed preview videos for the new series and the site ran a competition in which users could win a year's supply of Star Dollars, the currency used on the site. The competition was open only to children who had interacted with the bespoke scenery in Keke Palmer's office and created their own office space.
Natasha Lekka, digital account director at UM, admits the team was unsure how the Stardoll audience would react to having Nickelodeon characters on the site.
However, throughout the one-month campaign, which ended in June this year, 113,000 users interacted with the brand by watching the trailer, 9,200 visited the Keke page and 6% later clicked off the page to another element of the campaign.
In addition, more than 8,600 people entered the competition and 32,000 users interacted further with the Nickelodeon brand.
Nardis Roscoe, senior brand manager at Nickelodeon and Nicktoons, says: "Stardoll was a perfect platform and we were able to create a campaign that got members interacting in a way that isn't possible with most other forms of advertising. The level of user engagement exceeded expectations, with amazing results."
Bin Weevils: Party time in My Secret World
Brand: My Secret World
Media agency: Maxus
Lead planner: Daniel Parkinson
Imagine is a range of games for six to 12-year-old girls with the educational focus of helping players to work out what they want to do when they are older.
In a promotion for My Secret World, a game within the series, Ubisoft's agency Maxus launched an interactive campaign on Bin Weevils, the cartoon-turned-social-media-site that has been dubbed a "Second Life for kids".
The promotion began with visitors to Bin Weevils seeing virtual out-of-home ads for an online party, hosted by Imagine, within the shopping malls and outdoor areas of the community.
Parties on Bin Weevils take place in Slam's Party Box, an area that can be entered only when it is sponsored, and only by people of the age and gender specified by the advertiser.
For the My Secret World campaign, Maxus invited the target audience to a virtual party, where they would be represented by their online avatars and could interact with like-minded children.
The party was planned with the audience in mind - for example, it included a carefully chosen playlist, and was branded with My Secret World imagery. When users clicked on these creatives, they were taken to the Imagine website, with the promise of being given Mulch, the Bin Weevils currency, when they registered.
The party attracted 10,500 virtual revellers who stayed for an average of eight minutes and generated 77,000 impressions between them. The party attendance translated to a staggering 13% click-through rate to the Imagine site, well above average.
Daniel Parkinson, planner/buyer for Ubisoft at Maxus, points out that although the client cannot measure sales from this campaign - because children have no means of making purchases online - Ubisoft is confident the strategy was a success.
He says: "Social media is a strong platform to use and, judging by the performance of its ads last year, Ubisoft is very happy with the campaign."
Ubisoft is not the only gaming brand to use Bin Weevils this year - in October alone, there were four computer game campaigns running on the site.
Imagine's online spend was equal to just 5% of its TV advertising budget, yet the referral rate to its website via online activity was 40%, suggesting digital was easily the more cost-effective medium.