Well, she wasn't that small, but we just got home from the Alaska cruise and we had our 2 year old with us (as far as excursions, not much different from an infant in safety). We did the train ride in Skagway, although it lasted longer than expected (we booked through Disney because we heard this was a possibility). If you choose this, sit on the left - we sat on the right and when it's time for everyone to swap sides on the way back down, a huge annoying family didn't move, so my husband and I couldn't see much of anything throughout the ride.
We also did the helicopter tour/glacier walk, which was amazing! The helicopter almost lulled my daughter to sleep and we all loved the experience. I was a little worried about having a toddler there, but it was fine. She walked a little bit, was held through most of the walk, and seemed to enjoy it. We don't know if we'll ever be able to go on that cruise again, so we wanted to make the most of it.