We had a flexi ticket - that we could use all the Disney parks on any 7 days in 10. So we used both water parks (1 morning each) and went into the "rides" parks after on both days (1 straight away, the other in the evening). It also allowed us to go in for a while in the morning, go back to our apartment, and go back in the evening when it was cooler and quieter. The water parks were actually great, good pools, nice slides and relaxed.
DRINK YOUR WATER. All day. It's very humid and you WILL lose your rag (faster) if dehydrated. Let the kids run into the various fountains - they'll dry off in about 10 minutes. The restaurants etc will pretty much all give you glasses of water if you ask - but you need to ask. We used to get a coke or fizzy drink with lunch but also glasses of water, and also refilled our own water bottles at the various drinking fountains around.
If you have 2 weeks, you can get out into Orlando, and wider Florida. Kennedy Space Centre is a full day outing (we didn't even get the bus to the rocket park, as the Atlantis shuttle was only newly opened and took all our time). We also had a day doing a canoe/nature trip, which finished with swimming and picnic lunch (we had to bring our own picnic but they provided all the equipment), which was really interesting, DD loved jumping into deep water hole off a tree swing, we saw lots of wildlife and it was a lovely and cool, dim, and slow day. There are LOADS of other things to do - either other parks (Busch Gardens, Universal etc) or into Orlando or heading to the beach or into the everglades etc.
DD, aged 8 but short for her age, was too small for only 4 rides across all the parks (I can't remember the exact details now - but I had checked it out and knew which ones to avoid). But she did loads - all the Mountains, the "Tower of Terror" - the lot! And there are plenty of slower rides too that she still loved - like the teacups or Dumbo.
DON'T feel you have to rush around to see it all. Either decide beforehand that "we'll be back again sometime so we don't have to do everything" (even if it may be years away), or tell them that there won't be time to do everything so look themselves at the books (maybe get a kids book) and decide the things that they really want to see/do.
We didn't go for Princess stuff, dining with characters or things like that. Tended to bring in picnics and eat in the more "takeout" type food places (some were indoors with seating, some outdoors with seating, some just stalls to wander from); or else have a snack and eat later in a restaurant/back in the apartment. DO bring snacks in your bag in case people get worn out, and don't be afraid to take breaks and find quieter spots or shady areas. We went during 4th July (the busiest period) and DD has ASD/ADHD so difficulties with crowds/noise, and we got through with no meltdowns as we planned ahead - not set routes of rides to see (I know some people recommend that) but some rides we did want to see and checking maps either on arrival or in advance to see quiet spots or food places to make strategic retreats when needed.
Each park will give you maps of each park - getting one each is great. But the "tourist office" at the entrances will also have maps of the other parks. So either on your first day someone gets at least 1 map of each, or the day before you plan to go get the maps for tomorrow. Then you can look at them back in your accommodation at night, and see if there are rides you really want to go on, or character spots that might be worth stopping at etc.
Let the DCs bring an autograph book for the characters, and have a big sharpie type marker. Some spots, and charaters, are mobbed - others can be very quiet.
In terms of the parks:
Magic Kingdom - we loved and went in about 4 times, including afternoon parade. It's what most people think of as "Disney".
Epcot - we also loved and went in about 4/5 times, including the nighttime firework show. The trek around the world part was great, and had good food (german beers, olde English pub (the day Tim Henman won Wimbledon! so a good atmosphere, there were some nice sweet and bakery shops etc). And there was also a really lovely Christmas shop which I think was in Epcot, to pick up a decoration for your tree to remember the trip (they can be personalized).
Animal Kingdom - was ok. DD got the Park Ranger book to go around, look at various spots and get stamps and stickers. But we only went once.
Hollywood Studios - was also good although we only got there once. Has the Tower of Terror. Lots of good restaurants all along "Main Street USA", good playground area based on "Honey I Shrunk the Kids", and very cool shows of how they make movies.
Both water parks were good. We didn't go to the World of Sport (too much on otherwise).
And we didn't use our 7th day - we went into the Disney town shopping part instead of heading into parks. Really good lego shop (you can make up your own lego figures), figurines shops and souvenirs, bowling, cinema, and plenty of decent food spots.
Pace yourselves and it will be great!