Welcome!
I'm not sure it's really possible...
1) You are looking at driving 11.5 hrs straight through without any breaks to get from Calgary to Seattle. That's basically two days each way, which leaves you little time to actually do anything.
2) Seattle isn't on the ocean - it's well inland on a narrow bay. You'd have to drive farther to see the Pacific. Even the ferries run a route that goes inland of Vancouver Island, so it's not an ocean view (but gorgeous all the same).
3) There are no direct Seattle to Vancouver ferries - you have to go to Vancouver Island, drive to another ferry port and take another ferry to Vancouver
3) There are some adventure/water parks along the way, but the real beauty of Southern BC/Pacific Northwest is in the nature. Think swimming in lakes and hiking, not amusement parks.
4) I would check the US/CAN exchange rate - these days even discount shopping centres in the US may not be a very good deal. Plus if you purchase more than your important allowance, you will owe duty/taxes at the border.
You'd be doing something like this:
Day 1 - to Salmon Arm area (5+ hrs driving, think the Enchanted Forest is in the area)
Day 2 - to Seattle ( 6 hrs driving)
Day 3 - Seattle
Day 4 - to Vancouver Island
Day 5 - ferry to Vancouver, drive to Calgary (10 hrs driving)
You would not be on the ocean at all (you might have a very, very long distance view, depending on which ferry you take). There would be US shopping in Seattle, but places like Vancouver Island, Salmon Arm etc aren't shopping destinations (nature, gardens, biking, walking).
Note that all members of your family must have appropriate ID to cross the border. Adults must have passports, Nexus cards or enhanced driver's licenses (assuming you are all Canadian or US citizens). The kids, I think, can get away with birth certificates, but passports are highly recommended for less hassle.
