What haven't you caught that you want to try? Late March fishing can be pretty great depending on what species you want to chase.
If my children were still young, right now I would take them out for trout, walleye or Sturgeon. All 3 are fishing well, especially if you go with a guide who is on them every day.
For trout, most guides specialize in fly fishing. You might look around a bit to find one who specializes in bait and trolling. You may even offer to trade with one of the fishing fanatics on this site. They will have gear and local knowledge. You will get your youngster into multiple fish. And there isn't much better crappie and cat fishing than what I experienced fishing with friends in Oaklahoma if they want to trade a trout trip here for a warm water trip with you down the road.
The best walleye fishing right now is 90 minutes east of Portland. This is coming into peak season for the guides on that species. There are several advertising online. I would be sure to communicate that you want to cater to your 5 year old and wife. Maybe focus on trolling and bait. With a guides help they will get to reel a few in. This time of year they are getting more active and moving shallower to get ready to spawn. This is probably the best time of year to get into walleye.
Most guys do not think about Sturgeon during steelhead and salmon season because it is catch and release only on most water this time of year. The fish are less harassed and less wary right now. If you want to catch and release high numbers of these prehistoric fish now is peak time. An experienced guide will get you into 20+ fish in a day, and they will range from 30"-50" in size. The big ones, 4ft-8ft long show up later in the spring. If you haven't fished for sturgeon before that is what you should try. They are native to the Columbia River. Locals call them "The poor man's Marlin". They will jump. There are more in this river than anyplace I have ever fished. With a guide who focuses on Sturgeon it is the surest thing that requires the least amount of technical expertise from the clients. And some of the best areas are 30 minutes or less from Portland.
Let us know what you decide to chase after, and post a couple of pics of your fish on the blog when you get done!
Good luck to you!