fran,
I assume you've been to Disney before? Would you feel comfortable allowing your daugthers to go to a park on their own during the day and meet you somewhere after a few hours? Maybe that will make them feel more grown up?
My parents would allow me and my sister to do that when we got older. We went once or twice a year ever since they opened, so we knew the parks (only MK and later Epcot back then) really well and my parents felt safe with us there. (As a matter of fact, my senior year, when all my friends were going to Cancun, my parents and a friend's parents sent us to Disney - with the rule that we were "never to leave the World" - they felt it was a much safer option!
I wanted to book the pirate cruise for all 3 of our kids, but I figured dh and would have nothing to do for such a short time- not long enough to go to a park or anything.......