The answer for which ship is the smallest. The disembarking passengers can equal the population of a port town. Try to avoid that. So, absolutely stay off the Royal, Majestic and Discovery. Also no wraparound Promenade deck on these three.
Since you posted on the Princess board, you're looking for a Princess ship, yes?
The Sapphire is the best of given choices of the Princess fleet for Alaska, as it has an intact Skywalkers for viewing scenery. Grand had it removed.
Can't speak to kids programs, but there is a kids area. Very few kids on Princess. Last cruise, none, zero!