We've sailed Alaska with our son 3 times. He was ages 8-9-10. We sailed HAL, NCL, Celebrity. The kids programs were very similar on all 3 and they were all great. He had a great time on all 3 cruises. Since Alaska is a summer cruise there will be many kids of all ages. The clubs are sorted by age as well so kids are with other kids in their age group. Choose a cruise with the best itinerary and cost and don't worry about ships being kid friendly. They'll all be kid friendly.
Now about nature and wildlife viewing:
Take a whale watch trip in Juneau. Orca Enterprises (Capt. Larry) is terrific. You will see humpbacks and seals for sure, possibly orca, all very close up.
Also in Juneau take the bus to Mendenhall glacier. Besides the awsome glacier to be seen, if you walk to the end of the parking lot there is a bear viewing balcony over the creek. You may not see bears (we never did) but you will see salmon spawning. We were there in August. Note, it smells of dead fish too!
Bald eagles are everywhere. As you're heading to the whale watch or Mendenhall glacier, look at the marshes on the left of the road. If the tide's out there will be bald eagles all over the shoreline eating salmon. If you're lucky you'll see bald eagles sitting on light poles or on bldgs as well.
In Ketchikan, about a 5 minute walk from the ships is a salmon fish ladder. You will see salmon in the creek and also possibly jumping up the ladder. Take the funicular up to the hotel and walk down the married man's trail and you'll see some huge, gross, slugs on the ground too!
All of our trips were in August and we did spend a few days in Juneau once in July. The weather was almost always really good. You will get some rain along the way, that's almost a sure thing.
Enjoy the trip and wildlife.
