Our family set out with our neighbors a couple weekends ago to take on part of Mount Washington - a two mile hike to the Mount Washington Owl Hike Spot (with our kids in tow we weren't prepared to take on Mount Washington itself). This was our first hike up Mount Washington.
We parked at the Upper Twin Falls trailhead off I-90, and headed up the steep trail to the Iron Horse / John Wayne Trail. Heading west about 500 feet will take you to the unmarked Mount Washington trailhead. This is a very nice trail that meanders steeply upward through a lot of rock formations and trails. Occasionally you will get a glimpse of the Cascades through the trees, but generally there isn't a good lookout until you get to the Owl Hike Spot. The trail itself is a little rough - it is mostly small (about the size of a softball) rocks, which after 4 miles of hiking ends up being hard on the knees and ankles.
After two miles and a 1600 foot elevation gain, you will find yourself at the Owl Hike Spot with an amazing view of North Bend, Rattlesnake Mountain and Ledge, Snoqualmie, and Snoqualmie Ridge. The trail continues on to the top of Mount Washington (another four miles), but we didn't give that a try that day.
Books will label this as a challenge to kids, but they tackled it with a couple rests on the way up. There was also an amazing cave that rock climbers use for advance rock climbing. The kids (even my two year old, much to my surprise and worry) were able to scramble up it and have fun in the cave.