How lucky Mears! We went (pre dd a few years ago) - best holiday ever! helenmc is so right when she mentions a plan - know it sounds regimented, but if you don't, you'll get to the end of your hol and realise there is still so much to do!
We got our tickets when we were over there - don't really think there is that much in it. We got some of ours from our Virgin Hols Rep, as it worked out a bit cheaper. We were in Orlando for a week before going down to the Keys, so it was hectic! We visited Disney MGM Studios, Universal Studios, Universal Islands of Adventure, Epcot and Magic Kingdom. Of these, we found Epcot to be least enjoyable (tho' still great!), as it just feels a bit dated in parts - however, must stress we were there as a couple, and it's much more an 'educational' sort of place, brill for kids - the different themed 'lands' set around the Lake were amazing. Disney MGM was magic - fantastic rides, as was Magic Kingdom - there really is something magical about Disney Parks that Universal don't quite manage to replicate. Saying that, Universal studios was also brilliant, and Islands of Adventure (newest theme park) is truly unbelievable - leave it til later in your stay, as nothing else will quite match up to those rides!
We didn't go to a water park as dh doesn't swim, and would not have particularly enjoyed it, but they looked great. We saved a day and went to Kennedy Space centre - definitely worth a trip, especially with older children.
To save time on rides, you can register at automated machines within all parks, which gives you a 'ride time', so you avoid queues. This said, they even make queueing fun in Disney parks! Also try to catch an evening show at the Parks. We went to the film stunt show at Universal, fireworks at Epcot, and a 'Fantasia' show involving lots of water and lights at MGM - truly breathtaking. In somewhere like Epcot, it's nice to have a meal at the end of the day in one of the 'themed' restaurants surrounding the lake ie, eat at an English Pub (tho' quite why we'd want to in the US is beyond me!), Japanese, Chinese etc etc. We went to the Morrocan Restaurant as had been recommended, and it was very good, but we had to ring ahead to book it, as they get booked up. Also good in the evening is 'Universal City Walk', which is the strip between Universal studios and Islands Of Adventure - lots of cafes, bars, restaurants, shows etc, centred around a massive IMAX cinema, showing all the very latest releases (the stuff the UK can expect to see around Christmas 2003!) - worth seeing a film here for the cinematic experience, AND the boast you'll be able to make to your friends......'Spiderman? Oh yes, we saw that AGES ago!!...' Downtown Disney is also great at night, along by the harbour. More shops, restaurants, general nighlife and FUN.
You'll have a great time!