Boy... Seaside has changed quite a bit since the last time I was there. I think for a family, Seaside was more accommodating that Cannon Beach this time for us. It was not so touristy.
We ended up staying at the Seaside Wyndham's resort and had a blast. 2 hot tubs, kiddie pool and a main pool. All were very warm to hot. Even with the light spitting of rain, it was very comfortable. The suite slept 8, had a gas bbq on the patio and a full kitchen.
The worst run in was Pig-n-pancake. 45 minutes for breakfast for dinner was horrible.