Going to a NCL EPIC Eastern Caribbean cruise with 2 small children are they any beaches close by?

We will not be doing any Shore excursions. I know there is a beach by port in St.Maarten what about St.Thomas and Nassau? I'm nervous about taking a taxi I hate to be dropped off at a beach and no way to get back to the port. Also if anyone has used there taxi services what do they usually cost that way i know I'm not being ripped off. Thanks 8-)