Welcome aboard, Melissa! Any of the Port Adventures offered by Disney Cruise Line are sure to be amazing because Disney is great at choosing the best options and ensuring that they take care of all the details.
Each adventure listed on the Port Adventures page will list minimum age requirements. The Jeep Exploration in Cozumel has a minimum age requirement of 8-years old, so this will not be a good option for your family.
On that same page, be sure to choose "
Family Adventures" which will narrow your choices down to only those that children can attend. You'll want to look at the adventure you choose to ensure that your children can participate, as there is no wiggle room on the age requirements, unfortunately.
I assume that you must be on one of Disney's Western Caribbean sailings. If that's the case, I'd highly recommend the
Cozumel Beach Break. I was just there earlier this month and really enjoyed this beach at Playa Mia. It's a great choice for your young family!
In Grand Cayman, I can't recommend the
Boatswain's Adventure Marine Park enough! I can't wait to go back every time we visit Grand Cayman, it was that wonderful. My son and I loved interacting with the sea turtles, even getting in the tanks with them! There is so much to do at this park, I'm sure your family would really enjoy it. If you go, I highly recommend the conch burger for lunch! Delicious!
Have fun as you plan your adventures with Disney Cruise Line, Melissa!