We've cruised NCL out of both NYC and Boston and much - much! - prefer Boston. Parking is easier, embarkation is easier, it's just much more pleasant. I haven't been on Prima but have been on the Gem which is the sister ship to the Pearl. We found it a wonderful size, not too big but with enough activities to keep us well entertained. We got to Bermuda on Sunday on our last cruise and found lots to do. Everything in the Kings Wharf area was open and we enjoyed touring the National museum and the shops. I would think the activities on the Pearl would be perfect for a six-year-old. The Prima does have some extras but as others have pointed out they are more geared towards older kids.
As it happens, we will be on the Pearl to Bermuda for April vacation ourselves, with three teenagers who expect to find plenty to do 😉