oh boy that's a tough decision. All of these tours would be fun and interesting for you and your family.
Dunns River Falls is great fun, just make sure that you wear water sandals, water shoes or cotton tennis shoes with grip, as the rocks are slippery. There is a walkway alongside the falls if you feel that you don't want to make the climb, and if you start the climb and feel that you can't or don't want to contine there are outways. It is not a difficult climb, people of all ranges, sizes and shapes do it.
Jamaica is a gorgeous tropical mountaneous island so the ATV tour would also be a great choice.
Find out what class the rapids are, that could be a factor for your smaller kids, a better option might be the tubing tour.