Second Life members can visit the shack to buy a Yak for 1,000 Linden dollars (US$3.5). They can then milk or ride the animal or knit a woolly jumper, and enter a draw to win an interview in a Second Life magazine.
Second Life members can also visit the shack to make a donation to the charity. All proceeds go to the Save the Children wish-list, where people can buy gifts like school uniforms for families living in poverty.
The launch of the Yak Shack makes Save the Children the first UK charity to fundraise in the virtual world. The concept and creative for the project were developed by Ogilvy Advertising and designer Aimee Weber.
Kathryn Parsons, channel planner at Ogilvy Advertising, said the project aimed to "tap into a growing international community of young, creative and tech-savvy individuals".
She added: "It is an ideal environment within which to raise awareness, driven by its strong sense of community and shared values. Having collaborated closely with the Second Life community, we are confident we've created something that will deliver the kind of experience that's true to Second Life."
Chris Coe, product development director at Save the Children, said the charity was "delighted to be taking Wish List gifts to the next level by making them virtual".