The best Washington summer vacation to be had is at Campbell's Resort on Lake Chelan. About 3.5 hours from Seattle, Lake Chelan is the perfect little town for a weekend vacation. It's beautiful there in the Summer and Campbell's is the perfect place to stay. Right on the lake, with two pools and several hot tubs, the best rooms to stay in are on the bottom floor for easy access to the fun stuff. They just renovated and it looks lovely, but even if they hadn't renovated I'd be back next year. There's a full service restaurant and pub so you never have to leave (which is good because there's not many other restaurants in the area). There's also a Safeway just across the street which is nice because every year I forget my toothbrush. There are kids everywhere but in this magical land of Campbell's they are all adorable.
Be sure to hit Slidewaters, the best water park ever. In my next life I will have one of those retro blue and orange shirts that says, "Slidewaters Staff".