Norwegian Cruise Line was the only major cruise line to not charge for children aged 6 months to 2 years old.  However NCL has changed their fares for the young ones and they will be priced the same as other 3rd and 4th persons in a cabin.  Newborns that are not yet 6 months old are not allowed to cruise.

The first two passengers in a cabin are priced the same regardless of age on Norwegian.  Additional berths in the same stateroom will be at a discounted price, plus port fees and taxes.