Simulations are rule-based, player controlled spaces where inaction counts as much as action. Sims exist to play at building cities, families and to engage in restaurant wars. One "serious game" sim even puts you in the shoes of the CEO of McDonalds, pumping cows with hormones and clear cutting pasture to make your business more efficient (without Ronald's permission, I assume).
Some simple sim-adventure spaces for kids include Club Penguin (which has gotten way to commercialized since Disney bought it) and Funkeys, a doll tie-in game my 2 boys enjoyed for a long time, from UBsoft.
A really interesting link in her article was for GlassLab, a Gates venture, which is part of a site called Institute of Play, whose self-described mission is to "design experiences that make learning irresistible." Though I think the benefits are sometimes overstated, it's clear that experiential learning that spurs creativity and innovation are cornerstones of good learning, and that much of learning is, as Sugata Mitra likes to say, self-organizing (like the brain itself).
I'll be spending some time exploring the projects on the Institute of Play site, and report back.