Where are you coming from? Returning home or heading for Alaska after leaving Washington?
Most of the Olympic Peninsula is a rain forest. One thought to see Idaho would be to ride on the Amtrak Empire Builder to Spokane, spend the rest of the night in Spokane and then renting a car to see a small part of Idaho.
Driving across the arid eastern part of Washington just to see Idaho doesn't make sense.
I like the Oregon coast more than the Washington coast.
Alaska Airlines is a major air carrier from both SEA and PDX.

This is all over the place. Paging Suze and Janis.

I agree if you only have two weeks I would concentrate in the Seattle area, which could include Vancouver BC and Victoria.

I also think Portland would be a nice place with kids. There is a great foodie scene in Portland, but more importantly there is the Columbia River Gorge, Mt. Hood & Mt. Bachelor, and a short scenic train or drive over to the beautiful Oregon coast.

Because of the season, the trip should have a good portion of potential indoor activities, which suggests museums. However, a two or three day trip to the Olympic Peninsula could be in order, depending on the weather. Neah Bay has a nice museum of a village that was buried under mud about 300 years (or was it 500?) ago. Hurricane Ridge in Olympic National Park which gives a view of the Olympic mountain range might be snow bound.

Seattle, Victoria (a fantastic Northwest Native-American collection), Vancouver would be the cities to cover--no car needed, but passports would be a necessity.

Mt. Rainier can be a day's outing, again depending on the weather.

Go skiing for a day? There must be some ski resorts close to Seattle. But I do not know if there will be enough snow in April.

http://www.flickr.com/photos/mksfca/sets/72157622991196341/

http://www.flickr.com/photos/mksfca/sets/72157623130435790/show/with/8188806665/ These photos were taken at the Chihuly Glass and Garden in Seattle.

one thought....the Skagit Tulip Festival is April 1-30 so maybe a drive north to the Skagit valley, with stops in La Connor before heading over to Victoria or continue north to Bellingham and Vancouver BC.

There is also the Museum of Glass and LeMay Automotive Museum in Tacoma for a rainy day.

Think you first have to determine if you are going to take a once of a lietime type trip to Alaska.

If you don't do that - you have some good advice about what to do in Washington State - and here are a number of ski resorts within an hour plus of Seattle.

We really liked Crystal Mountain - a very nice area on the back side of Mt. Ranier - that now at least - has some good snow - with a base of 92" in places. http://crystalmountainresort.com/The-Mountain/mountain_report and http://traveltips.usatoday.com/ski-resorts-nearest-seattle-washington-51137.html

And if you do want to visit Idaho - Sun Valley is beautiful and a great place to ski/hang out. http://www.sunvalley.com/

It's about a 10 and a half hour drive from Seattle - but you could break it up - and maybe also explore Boise for a day/night on the way - or on the way back. http://www.travelmath.com/driving-time/from/Seattle,+WA/to/Sun+Valley,+ID

And if it's relatively clear - you could also drive along the beautiful middle fork of the Salmon River over to Mc Call Idaho - and visit Tamarack resort - but there is also has some other good skiing around there. http://www.skiidaho.us/resorts

You could also take a shorter drive from Seattle over to Spokane (4 hours) - and see the beautiful lake/resort at Coeur D'Alene, Idaho (another half hour) - and maybe ski in the "Little Switzerland" area of Idaho - at Schweitzer. http://www.schweitzer.com/

You could also fly from Seattle to one of these places.

BTW - you could also take the train/Amtrack from Seattle to Schweitzer - and what a beautiful ride that would be. http://www.schweitzer.com/plan-your-vacation/getting-here/by-train/

Such great advice already, thank you all so much.

I hadn't thought to mention skiing in my original post, mainly because we don't ski. We are Floridians and while I am not ruling out having my kids learn how to ski, I will wait until they are older.

@tomfuller - we would be coming from Florida and the trip to Alaska would be round trip from Seattle as we plan to fly out of SEA at the end of the trip. You also bring up a good point about the drive through Eastern Washington.

On a somewhat related note, @tomsd, this is definitely not the full "once in a lifetime trip" to Alaska. It would be just to visit Anchorage. I think you bring up a good point - put off Alaska until we can do it right. I was thinking we would go to Coeur d'Alene if we went to Idaho. Since we don't ski, it sounds like Little Switzerland is out. Am I right in thinking that any place in Idaho that is known for skiing is going to be covered in snow in mid April? I need to see if Coeur d'Alene will be as well. I don't mind snow, and goodness knows the kids would love it since it is such a foreign concept, but there's not much to do with snow unless you ski! My kids would love the train but knowing my husband, he will want the convenience of driving.

@michael, thanks for the tips on the Olympic Peninsula. We plan to drive regardless of whether we need a car but it is nice to know that Vancouver is walkable. We have passports for the kids as we are going to Europe with them in a few months.

@nanabee, thanks for the Oregon suggestions - while Portland doesn't interest me much, Mount Hood and the Columbia River Gorge do.

@POlson, thank you for recommending the Tulip Festival. That would certainly be something we would check out if we head up to Vancouver.

Again, thank you all and I welcome any additional suggestions. While I have not narrowed down my options yet (except to nix Alaska), I have a clearer idea of the pros and cons to each option.

Since you are concentrating on Washington, you should visit the town that resembles Bavaria. http://www.leavenworth.org/modules/pages/index.php?pageid=1
Leavenworth has things going on most of the year.
Bend Oregon won't have much snow in April but if you want to see it, just head up to Mt. Bachelor.

A couple of thoughts/points/reality checks:

April in Alaska is arguably the worst time to visit (most areas; it's a gigantic state.) In Southcentral Alaska (Anchorage, Kenai Peninsula etc.) it will still be wintry or, worse, "breakup" - when the snow melts, revealing the winter's accumulated debris and junk. Then everything turns to mud. In interior Alaska (Denali Park, Fairbanks, etc.) it will still be winter; the interior of Denali NP typically doesn't even open until June. Southeast Alaska (the "panhandle" - Juneau, Ketchikan, Sitka etc.) will likely be wet and gloomy, although a bit less predictable than other areas. Throughout Alaska you'll still be 1-2 months early for any tourist attractions to be accessible.

The same goes for the high country in the Cascades. In April there will still be 5-10+ feet of snow on the ground at the Paradise visitor center on Mount Rainier, and getting there will almost certainly involve having to use chains, something most rental car companies oppose.

What to do instead? Well, the Olympic Peninsula is obviously a good choice, although the high country (Hurricane Ridge) will have the same issues at Mount Rainier etc. The tulips and daffodils in the Skagit Valley are lovely, and can be done as a day trip from Seattle (combined with a drive up/down beautiful Whidbey Island.) http://gardyloo.us/DSC_0077c.JPG

Another option might be to do a big loop through the Palouse country in SE Washington and back through the Columbia Gorge. In the spring, the rolling Palouse hills are covered in new wheat, and the lighting, the incredible shades of green, the red barns and white farmhouses - it's really a stunning display. http://whiterivergallery.com/blog/wp-content/uploads/2011/03/0069.jpg (BTW it's where Apaloosa horses got their name.)

The weather on the east side of the Cascades is generally much dryer than on the west side, and probably warmer, too. It's a marvelous spring tour.

You could extend an Eastern Washington drive to Lewiston (Idaho) and Clarkston (WA) then return via the Columbia Gorge. Again, in the spring the melting snow from the mountains will fill the many waterfalls along the Oregon side of the Columbia Gorge to a spectacular degree, and areas like the Hood River Valley will be full of blooming fruit trees. If you want, you can run up to Timberline Lodge on Mount Hood (where they'll still be skiing) if the kids want to "go to the snow." And at the Bonneville (dam) hatchery, the kids can see the huge sturgeon (including 100-year old Herman the Sturgeon) as many previous generations of kids have done.

Gorge: http://gardyloo.us/20100509_5a.JPG
Hood River Valley: http://gardyloo.us/20100509_85a.JPG

This is a great Pacific NW loop - mountains, wheatfields, waterfalls, high desert, Indian reservations... great for the whole family.