We loved the St. John's eco hike. It wasnt a hard walk, they give you a bottle of water. Our guide was very knowledgible of the local history and very friendly. You also visited the remains of an old sugar mill and got a few minutes to swim on a small private beech before returning to the ferry boat. One thing to remember is that the ONLY bathroom is on the ferry boat. So best to use it before and after the hike.
The butterfly garden tour is great for kids, especially the younger ones, however in December there were butterflies all over the island to see anyway.They must have just hatched out recently. We did the historical tour of both sides of the island, but wasnt really impressed with it. We did have 2 spectacular views of the islands, but the drivers were so crazy( no seat belts either) that just surviving the excursion was the highlight! Also bathrooms are far and few between, no water fountains anywhere on the islands, so pack your own water, they do sell it as you get off the ship. Usually there will be one public restroom to use 1/2 through the excursion and 10 minutes for 100 people to use it. If you just walk around and shop you will have to pay to use a public restroom unless you use one in the casinos, they are free. Remember their standards of cleaniness arn't the same as ours. Just a warning. Our kids did the snorkeling tours they offer at each island and loved every minute of it, the guides were very friendly and were eager to teach you if you were a beginner. The last time we went, we just walked through the shopping area at a leisurely pace, that was very nice too.
Hope this gives you a couple of ideas.
mom x4,grandma x4