4-5 days would be Seaside, very east coast in flavor, close to Astoria for movie shooting area tours, docks with sea lions, fishing boats. seaside is an easy tour city, many streets. movie theatre. carnival town.
cannon beach is hard to travel, single lane traffic and not under 16 friendly for entertainment. can day trip to tillamook.
Newport has many family activites for a 4-5 stay, but then I assuming if you are a family, what is your make-up...that makes a big difference in choices.
I can help you with more info knowing who you are and expectations? each city has its own adult and child advantages?
oh, i see above it says family....Newport has best seaport north of frisco, two sea museums, working dock with amusuemnt factors. lighthouse,, two different style of beaches, south beach is flat sand dunes, north beach is cliffs and narrow.
Lincoln city starts in middle with lodging flush with beach, but travel south or north and lodging is on cliff with hard access to beach. Newport has no lodging with beach access. Seaside is total beach access, cannonbeach have to drive to beach. There is nothing friendly in northern calif for beach access.
none of these cities have any convivence access to valley, except florence, easy fun drive to Eugene, a fun city to explore. Salem in wnter is dead, PDX terrible drive