With a number of news stories lately about kids under 13 on Facebook (on the site against the social network’s terms of service), you’d think there weren’t any other social networking sites that were geared for kids or where kids wanted to be. That’s hardly the case, as there are many social networks, gaming sites and virtual worlds aimed at the under 13 set. In fact, a study last year suggested that of the billion some-odd users of virtual worlds, over half are under age 15.

One of the newest kid-friendly sites is MiniMonos, a New Zealand-based company that, just six months after its launch, already has over 250,000 users. That’s dwarfed, of course, by the popular Disney-owned Club Penguin, with over 6 million monthly active users. While MiniMonos is similar to Club Penguin and other virtual sites with its emphasis on fun avatars, games, and virtual goods, MiniMonos, which means “little monkeys” in Spanish, is unique in a couple of ways.

Although MiniMonos isn’t an educational site per se, smart content is integrated throughout the virtual world, much of it focused on caring about the planet. WIth their monkey avatars, kids engage in a number of sustainability games and lessons. For example, kids play recycling games that keep their treehouses tidy and cloud collection games that help generate wind power. Moreoever, they learn the environmental consequences when they don’t keep up on these tasks (Messy house, no power). Kids can also play TicTacPoo… because, well, they’re monkeys, and poo is hilarious (and compost helpful).

Flinging poo may be a game that appeals to young boys more than young girls and MiniMonos certainly seems to be aiming at that demographic more than some of the other fashion-focused virtual worlds.

But what makes MiniMonos different may well be its commitment to linking the online world with the offline world. The site hopes to demonstrate that sustainability isn’t just about maintaining the virtual environment and in-world actions on MiniMonos lead to real-world results. MiniMonos has partnered with a number of environmental groups: supplying clear water in India, adopting two orangutans through Orangutan Outreach, and supporting WWF’s international Tiger Initiative.

It isn’t simply linking gaming with a social cause – that’s pretty common for kids’ and adults’ sites. MiniMonos also has launched an “EcoMonkey” program that provides kids with in-world rewards for their real-world eco-actions, such as setting up recycling programs at their schools.

Although there are plenty of other sites that have environmental science education components or that encourage kids to get involved socially, MIniMonos integrates this eco-sensibility throughout the gameplay and it ties kids’ actions offline to their online presence. That commitment to offline activism is crucial to the startup’s founders, many of whom, including CEO Melissa Clark-Reynolds, have been trained as Ambassador for Al Gore’s Climate Project.

MiniMonos recently announced that it has been accepted into the Springboard accelerator program in Cambridge, England.