Roblox has raised roughly $2.2 million in funding for its virtual world/casual game hybrid, according to an SEC filing. Altos Ventures and First Round Capital participated in the round, per VentureWire.

Roblox lets kids socialize, play games and build their own virtual environments; many of the games on the site were created by the users themselves. Currently in a public alpha phase, there are some branded games (like “McDonald’s Tycoon”), but no other ads.

A premium membership gives kids more access to games and other extras for about $6 per month. The Redwood City, Calif.-based startup has been up and running since at least 2006.