Atlantis Junkie & Mother of one son, age 6. Take my advice - purchase the Carnival Excursion "Atlantis Aquaventure" and be prepared to have the time of your life. You get to do everything (Dig, Waterpark, etc.) plus they pick you up, drop you at Atlantis and bring you back.
Don't try to do this on your own - pay the price and be prepared for your grandson to have an AWESOME time with minimal planning on your part. WELL WORTH THE $$$. I do it everytime we cruise into Nassau.