I apologize it took me a bit to reply. I meant to get on here this morning, but things happened. We took a
Royal Caribbean excursion to get to the island, but it is very easy to catch a taxi to the ferry dock and going over that way. We looked into it because we were going to come back sooner than we were scheduled to on our own, but my dad is very hesitant about doing anything not done by the cruise lines (Don't ask.).
Down by the private ferry dock (right by the national park building), there is a "hiking" trail (really stairs) that climb up a hill and back down that take you to a nice beach that isn't crowded at all. There weren't chairs or other amenities, but it was very pretty. In the other direction (more toward downtown), there were several restaurants that had a "beach" area that some people dipped their toes in or swam in. That one wasn't really my taste. I was thinking it was probably a polluted area (just a guess). It is near this downtown area you'll find taxis that will take you to the beaches. A couple that we met did snorkel here. They said it wasn't bad and that they saw a few things. Overall, St. John's will be less crowded than St. Thomas.
DS' favorite part was the boat ride over. It was neat seeing the different islands and finding out that you could buy your own private island for only $15 mil. I'm sure we'll all rush out and get one. The yacht club was neat too. They start grooming the kids for sailing at age 3.
There are some good little restaurants there. There were some ice cream places too. We liked one of the sandwich shops that was tucked away in the shopping area across from the national park building. I will go back and look at my stuff to see what that place was called. We did find wi-fi there, but it wasn't the greatest.
I hope this helps. Let me know what else I can do. I will go back too and look at the beach info I have.