At Harvest Caye you will be able to walk off the ship shortly after it docks. And, you may return to the ship, or leave the ship, as you please (multiple times if you wish). You might choose to pay to eat on the island, or, you can return to the ship for lunch/snack, and go back out to the island again.
People complain about the walk, yet it is approximately a quarter of a mile to the entrance.
Trams are available if you choose to wait to ride one.
The island itself is approximately a mile long (yet, not all of that is assessable to everyone!
It might be very hot there! However, there are misting tubes throughout the nature cages/displays which offers the chance to view some animals, birds, and plenty of lovely plants.
The island does have some shops offering Belizean's goods.
Hopefully, you will enjoy a wonderful day. Use sunscreen, early and often!!!