Club Penguin now has more than 15m members
For many years the average video gamer has been male and aged 24 or more.
These young men typically have the disposable income and time needed to support a gaming habit and, it has to be said, many of the titles being released were designed to appeal to such folk.
But casual games and the appearance of the Nintendo Wii have changed that profile and now it looks like it is about to change again.
Research suggests that there are about
158 online games and virtual worlds in development or up and running designed specifically for children.
While some of that total are recognisable games, most should be classified as virtual worlds, said Joey Seiler, editor of Virtual Worlds News, who drew up the exhaustive list.
Although these worlds, such as Club Penguin and Neopets, have games in them they are more an environment children can explore via their avatar.
"There are things to play with, like monkey bars or virtual snowballs, but it's up to the kids to figure out what to do with them," said Mr Seiler.
Some virtual worlds are hugely popular. Habbo has 90m accounts, Neopets 45m, Club Penguin 15m and Star Doll 15m. All these virtual worlds are aimed at children under 13.
VIRTUAL WORLD NUMBERS
Habbo - 90m accounts
NeoPets - 45m accounts
IMVU - 20m accounts
Club Penguin - 15m accounts
Star Doll - 15m accounts
Gaia - 12m accounts
Barbie Girls - 12m accounts
Source: K Zero
For Mr Seiler this popularity is based on three factors: friends, freedom and fun.
"One reason virtual worlds are extremely compelling is that they offer a way to get out of the house and reconnect with friends after their curfew hours," said Mr Seiler.
The virtual worlds also give kids great freedom to express themselves.
"For kids, though, when they don't have as many options in real life to decide what their house looks like, what type of clothes to wear, or where they go, virtual worlds must seem like a whole new land of opportunity," he said.
Finally, he said, these virtual worlds are enjoyable places to be.
"Successful virtual worlds encourage creativity, imagination, and fun," he said. "That's pretty appealing to any kid."
But, said Lane Merrifield co-founder of Club Penguin, creating a game that appeals to children is not easy because they are both technologically adept and very critical consumers.
Respect for the audience, said Mr Merrifield, was vital for that success.
"If it doesn't matter to an eight-year-old it shouldn't matter to them," he said.
Many virtual worlds aimed at children are tied to toys
"Kids are so perceptive," he said. "Those that enter this space for financial or business benefits, I think kids are going to see through that and there's potential for them to shun those products."
Mr Merrifield added that while children had to be engaged by the world, there was also a job to do to re-assure parents these places were safe.
Club Penguin has a limited chat system and a large number of moderators monitoring interaction in the virtual world to ensure there is no inappropriate contact.
Karla Buchl, a spokeswoman for Burda:ic which runs Hello Kitty online in Europe, said all those overseeing virtual worlds aimed at children had a duty of care for their users.
"It's in our interest to have the sites stay safe," she said, "given our target groups we really need to do that."
But, she added, virtual worlds had to walk a fine line between giving people enough freedom to communicate and limiting the potential for abuse.
Bought and sold
Beyond safety many parents are also worried about the commercial connections of many virtual worlds.
Nic Mitham, head of the K Zero consultancy which watches this industry sector, said entry to many of the virtual worlds was via the purchase of a toy or game.
For instance, he said, the Barbie Girls was won when a child got hold of the Barbie MP3 player. Similarly access to Webkinz is based around purchase of a soft toy.
That trend was only going to grow over the next few years, he said adding that soon it would be hard to name a toy that didn't have some kind of web content associated with it.
Partly this was a marketing move to engage children with the products they buy or get as presents but equally, he said, it was one of the few ways available to generate cash from virtual worlds.
Lego Universe will builds on the success of other Lego video games
To pay their way some virtual worlds, such as Club Penguin, offer access to more content for a small subscription fee.
Others use adverts on a home page or portal to offset running costs and some use make money by asking users to pay for the virtual goods used to adorn their in-game homes or avatars.
But, said Mr Mitham, there was no doubt that this stampede to entice children into virtual worlds associated with products, be they books, soft toys or films, would create casualties.
"I expect to see the first signs of fall out next year," he said. By that time the seed cash from venture capitalists behind many of the worlds will have dried up and it will be obvious which ones have managed to grab a significant audience.
"We will see some worlds closing and some acquisitions take place," he said. "In the place of the more generic virtual worlds will come those allied to a particular genre or interest group - such as Lego Universe.
For Mr Mitham there is nothing virtual about this phenomenon.