First cruise, three nights - port adventure in Nassau or stay on ship

[Momtotwo15]

This will be our family's first cruise. We are doing a three night cruise on the dream. Our daughters are 4 and 6 and my oldest daughter loves dolphins. Trying to decide if we should do an Atlantis or blue lagoon dolphin excursion in Nassau or stay on the ship? I know three days is not enough time to do everything but want to do as much as we can