Imagine an online community with the cuteness of Hello Kitty, the collectability of Pokemon, the personal pet care of Tamagotchi and the sociability of Facebook.
The thought conjures dollar signs and that great quote from Facebook movie The Social Network: "A million dollars isn't cool. You know what's cool? A billion dollars! And that's where you're headed; a billion-dollar valuation!"
"I'm not sure if we're quite in Facebook's league just yet," says Michael Acton Smith, the modest creator of children's website phenomenon Moshi Monsters. "But we are certainly one of the biggest digital brands for kids."
What's happened since Smith - aka "Mr Moshi" - launched it in 2008, has been a phenomenon. It has 87 million children moshed-up across 150 countries, with some 7.5 million monsters adopted Down Under. Toys, books and video games have followed offline. Now there's a stand-alone movie.
Moshi Monsters is a free, safe, social online world where children (aged about five to 12) adopt their own Moshi Monster. They solve puzzles to customise and care for it with food, furniture, treats and toys. They can also make friends with other owners, leave messages and create communities. The puzzles get harder or easier according to the child's results.
"I loved puzzles and treasure hunts as a kid," explains the polite, erudite and very English Smith, who was recently awarded an OBE on the Queens Honours List.
"My favourite book as a child was called Masquerade, where you had to solve these clues on a treasure hunt. I thought there weren't those kinds of experiences for kids online. And whenever I invent a business I like to look for areas that aren't ultra-competitive. So I felt this was a big opportunity."
But it wasn't all smooth sailing for the 39-year-old entrepreneur. He spent two years creating other games, including Perplex City, and went bust several times.
"I urgently needed a new idea that might appeal to broader audiences and realised how much kids loved technology and the web. So I tried to create an environment for them online, and that's how Moshi Monsters was born."
What started with Smith doodling simple little critters quickly grew into a company with 200 employees.
But even then, Moshi Monsters took a while to catch on. "It went live in 2008 but it wasn't an overnight success. Nothing really happened for the first 18 months, which was quite heartbreaking. Kids didn't really seem to engage and we came close to throwing in the towel several times. Then in the summer of 2009, we cracked the code."
That breakthrough, Smith explains, was adding social networking to the site.
"Kids love to be social. They love to share and show off. So if we could build safe community tools that allowed them to do that, we knew we would have something really special. And without doubt, that's the biggest single factor in the site's success."
Smith, who lives and works in London, admits that bullying can still occur on the site, with some children writing disparaging messages to others. But both computers and humans constantly check for anything untoward.
"I think the social aspect of Moshi Monsters is also a great training ground for kids to learn about online communities before they progress to sites such as Facebook or Instagram or Snapchat."