Cruise excursion with kids in hawaii?

We are taking a cruise to hawaii from san diego,with 8 sea days and 5 days visiting the islands in April. We are taking 2 kids age 13 & 4 at the time of cruise. Does anyone have any suggestions on what we should do while in port? Since we have our 4 year old I was thinking we may just rent a car. We will be visiting Hilo, Maui , Honolulu, Kona, and Kauai. This will be the kids first cruise, our second, and first time to hawaii. Thank you!