1. What cruise lines work best for 7 year olds (for either destination)?
2. Will they be bored at the ports in Alaska?
3. We would like to do a cruise that starts and ends in the same place. Since the ship wouldn't go as far north, would that limit our chances of seeing whales, eagles, bears, etc?
4. Can you see wildlife from the ship or only on land tours (except for the whales of course!)
5. If we head to the Carribean, any suggestions on what ports would be best for kids? Any to avoid?
Since cruises to Alaska are often family affairs, any cruise line will work for the 7 year olds, except maybe Holland America. I'd go on price. We used Royal Caribbean last year. Princess has a long history in Alaska. Alaskan cruises are more about the tours than they are the ship.
Will the children be bored? It will depend on the port. Some are more about the scenery than anything else. But they might like the dog sled tours offered, perhaps the train ride in Skagway, seeing a glacier.
Seeing wildlife is hit or miss. No guarantees. We saw seals and otters from the ship one evening, whales and sea lions we saw on a tour. However you could easily be in a situation where you saw whales from the ship. Don't expect to see humpbacks leaping from the water. You'll most likely just see them skimming the surface for a few seconds.
Caribbean? I wouldn't say "avoid" any ports. Just that some are best if you use a ship's tour and not venture out on your own (think Jamaica). Kids like Grand Cayman because of the turtle farm.
I wouldn't dwell too much on trying to please the kids. Kids usually find a way to have fun no matter where you are. Think of what you want to get out of the cruise too.
We had a fine time doing a round trip out of Seattle for last year's Alaska cruise.