Personally I would use a towncar vs the taxi since your traveling alone with kids. With a towncar you can make arrangments in advance have a confirmed price and if need be help with your bags. IME the town car cost is the same or less than a taxi. We like Tiffany but there are lots of great services recommended here, just do a search for town car recommendations.
You can also use Mears Transportation for a shared ride, you will be in a bus or van with others and may stop at other resorts prior to the Dolphin. One way cost is $21 for adults and 17 for children 4-11. Although if all the kids are over 4 then the cost is about the same for the shared Mears ride as for the Towncar!