I have yet to assist a family with outdoor preschool, but find the concept very interesting and look forward to following this "new to Seattle" development. Check out the link below for an NPR story on the concept.
I have a good friend that was an American expat in Norway and one of the things that caught her off guard was the amount of time her preschool children spent outside - rain, shine, snow or wind. Being outside was a big part of their preschool day and they quickly adjusted to bundling up to eat their lunch in the wooded area on school grounds - snow or no snow. To say the least, she didn't join them for lunch too often! Kids adjust quickly - parents, it seems, sometimes take a little longer.
I also thought it worth sharing this recent article from "The Seattle Times" about an outdoor preschool program setting up at the Seattle Arboretum - June 15, 2015