Tough one...the good thing about a cruise is your children will have new experiences and make new memories. I believe they will have a great time on the Fantasy. I've been taking my grandson on cruises since he was 8 years old and now that he is 19 years old, he constantly talks about the great moments that we shared on our cruises together and is still sailing with me whenever we can. Not to downplay a Disney vacation because I am a Disneyholic BUT the ticket prices have increased, food at the theme parks is always a budget buster for a family even with the dining plan, not to mention snacks, souvenirs, hotels, mouse ears, etc. It's all the ancillary expenses at Disney that can break the bank. Also, when you are at Disney, you spend exhausting days in the theme parks but don't quite experience the quality time you would have on a cruise vessel even if the girls went to Camp Carnival. I think you have to go with your gut on this one. I only live 15 minutes from the Magic Kingdom and go quite often because I have a Florida resident annual pass, however, I believe cruising is an adventure they will never forget and a great shared experience. August is very hot and humid in Orlando and makes for a tough day of trudging around the theme parks.