Although we leave for our first Alaska cruise in 5 weeks, we have spent a lot of time in Vancouver and the Victoria area, always in August. I can help with those areas now, and when we get back, I will get my 9 year old to make suggestions for the rest of the Inside Passage. In the meantime:
Vancouver is a great town. You can easily spend a week here. The Capilano Suspension Bridge over the canyon was just a little road side stop in the '80's. When I was their 3 years ago, they had monopolized on the bridge, and created a tourist attraction around it. I'm sure some people would say "trap" but it was a very good quality lttle park with native dancing exhibition, great views, and a very good gift store, along with historical photos of the time it was built, etc. I've tried twice to walk across the 6' wide bridge and haven't made it yet! It's perfectly safe, but I can't convince my nerves of that. GasTown in Vancouver is really good for walking around for a day. Stanley Park is a huge public park with a Totem Pole area (about 12 poles), a huge area where Canadian geese flock in the hundreds, but watch your step! And the Aquarium is fabulous. Very good exhibits and shows of sea otters, beluga whales, porpoises, etc. Kids will love the park. Hiking trails, etc. Grouse Mountain by tram was a good 3 hours spent, too. Great views of the area.
A day to Whistler was definitely worth the 3 hour trip up the mountain. Where we are from the biggest hill is the freeway overpass. So taking the tram up the ski gondolas to the top of the mountain, where they still had snow in August, was thrilling. They have a mountain bike race down the slopes in August, and it was great watching those nuts go down the rocky mountain as we sailed over them. Another twin mountain peak next to Whistler had just stopped skiing two days before we got there, so August 6th or so!
There is a huge ferry that goes from about 45 minutes south of Vancouver over to Vancouver Island, with Victoria to the south of the island. On the way to Victoria, you MUST stop at Buchart Gardens! The only description for Butchart is incredible. 7 unique garden styles maintained by over 150 gardeners. Sheer perfection. Even my son, who was 6 at the time, really liked it.
In Victoria, there is a glass conservatory that is pretty cool. Just walking around the harbor is great too. I doubt the kids would go for the Empress Hotel Tea. And too expensive anyway. We went on a whale watching tour from the Victoria harbor because they have some resident Orcas, but save your money and go out of Juneau where they guarantee you will see them. The Natural Science Museum near the harbor is a really good museum. Don't miss that one. They also have IMAX nature films there.
As I said, I'll write more, especially from the kid perspective, when we return.
Don't drive yourself crazy; that's a long time to wait!