We started cruising as a family when my boys were 5 and 8. We always did shore excursions together and they enjoyed Camp Carnival while we were on the ship.
Starting when they were 9 and 12, we would do family excursions in the morning and then take them back to Camp Carnival, so that Dad and I would go into town for some shopping.
Now they are 14 and 17 this summer in Alaska the boys took themselves back to the ship at Ketchican, after our family outing, while Dad and I shopped around town.
Dad and I have never gone on any "shore excursions" without them, (I would not feel comfortable doing that) we do go into town shopping and I see absolutely nothing wrong with that. We have never had a problem.
The boys no longer do much with Camp Carnival, but that is their choice.
It is like anything else, all you have to do is use a little common sense.