Very nine state campground
Tons of frees. Plenty of walking spaces, hiking trails and a large lake and dock. There's an "environmental learning center" and plenty to keep kids busy.
Tent sites in the trees are some of the best for privacy. Trailer sites are more in the open but have plenty of space for backing in as well as electric hook-ups, fire pits, and a dump site.
Close enough to Seattle or Great Wolf lodge to be in a good location, and far enough away to feel like you're away from the cities.
Month of VisitMarch