I just got back from an Oregon trip with the family and I can echo what Sean said, including the outstanding beaches and parks. I would spend every hour of every day at a beach if I could, so the Oregon coast is in my sweet spot.  We spent most of the time in or around Seaside (35C temperatures drove us out of Portland the one day we attempted it).  The weather was perfect, sunny and the low 20s.  Oregon is definitely the place to go, particularly with young kids, for a summer holiday.  Among my daughters’ favourites were the bonfire on the beach, bumper cars, and the vintage carousel. 

At left is Ecola State Park, my favourite stretch of sand.