From a Trip Advisor article about this excursion (Allen Marine is who HAL uses). Doesn’t sound like it would be enjoyable IF HAL would even allow an infant.
Age Restrictions We welcome guests of all ages onboard but like to give parents travelling with younger children additional information about the tour. Most infants and toddlers become very unhappy on this trip due to the long tour length and boat size. There is not much room to roam around inside, but there is walking space outside on the observation decks. This space is exposed to the elements and rather cold. Please note: there are no changing tables available, and there is no room for strollers onboard. While there is no charge for children two years old & younger, all guests must have a ticket due to coast guard regulations. Please call our office to make a reservation if travelling with an infant.
https://truealaskantours.com/tour/tracy-arm-fjord-glacier-explorer/