Taking our first cruise May 12th inside passage Golden Princess. Trying to decide best excursions with 4 1/2 and 2 yr. old kids. Need to consider length of tour and afternoon napping. Any advice would be appreciated.

Take the railroad excursion (Whitepass Railroad??) if you stop in Skagway. They can at least sleep in the train if they get tired. You will get a great scenic trip. Whale watching is also a good one. They can stay inside the boat and watch/rest while you get to see the whales.

Eventhing else might be a bit much for that age group (lots of hiking and such)

I agree with Jim the train ride is a must.
In Ketchikan we did a Rain Forest tour. There was a couple with a stroller and a 4 or 5 year old. They had no problem. The kids loved the petting corral at the end of the trail.
This link will take you to my RainForst photos.
http://joslin-family-photos.smugmug.com/gallery/2612414#P-3-15
Links to other photos are below.
Have fun

I agree with the train and the whale watching for sure. In Ketchikan you can take them on a horse-drawn trolley ride which is fun. We also did the rain forest there, as well as a ride on a duck. The duck and trolley go about the same places except of course the trolley cant go out on the water. In Sitka we did a rain forest walk, it was a wooden trail and easy for strollers. We like to just walk around town as well. Have fun, you will love Alaska. I want to take our 3rd cruise up there in 2008.

Ducks in Ketchikan, Train in Skagway, and whale-watching or fishing in Juneau... all great choices for kids.

One note about the boat trips: Be sure the boats and crew are "family friendly"... some smaller charter boats have grumpy old captains that don't like (or allow) kids. Other charter boats are family operated and have plenty of games, coloring books, dvds, iPod hookups, etc. to while away some of the slower minutes.
If nap-time is a concern, look for a smaller boat with a cabin and good sized bunk. Something about the vibration of a boat's engine and gentle rocking on the water seems to put kids to sleep every time!
My kids get bored on the larger boat trips with too many people around. I guess they get over-stimulated with so many folks, and it's hard for the shorter ones to see over the rails when 15-150 other folks are trying to take their photos.

Have fun!

-Case