We had a great time at Grayland Beach State park last summer! One day just sand as far as you can see, the next day tons of seaweed and other stuff to explore washed up on the beach. Note the coat on my little one though, it was August and not very warm, although I think we made it down to sweatshirts the next day
We are booked for 4 days in August and are staying on the dunes this time (nice new bathroom/showers in this section of the park) The Long Beach kite festival is going on at the same time and we will make the trek south to take a look.