Congratulations on your newest cruiser!
Our daughter was 20 months when we first returned to cruising. Check NCL terms of service would be my first recommendation. It’s tough with a little adventurer in terms of pool time as you need to be potty trained. Staff will help a lot with removing diapers. Our daughter didn’t quite get the cruise thing to start, by end of the week she was lining up for kids crew. We planned excursions to where she would be able to engage (Disney World and hotel pool day). The Disney is one of our favorites.
A lot may have changed since we first went as that toddler who rode on top of my shoulders all day at Disney is now a sophomore in college and Platinum with NCL. Babysitting may be tough to find, though the bright lights and people on the ship can be entertaining. Beach days were easy days. We also planned the first cruise with minimum ages so she could attend kids club. The crew was wonderful with helping on food, even finding a chafing dish of macaroni and cheese when she was having a day.
Both Boston and New York are readily accessible by car (park near or on the pier depending).