It depends how old your kids are and whether or not they are big enough for the thrill rides (and if you and DH want to do them anyway even if your kids are too little). It also depends when you go.
If your kids are preschool or early elementary, you probably will want two days at MK. We always spend at least one full day and often parts of many other days at MK. We spend one day at AK (till mid afternoon, then we go somewhere else), one day at DHS (once again until mid-afternoon), and one day at Epcot (although it deserves more time, but my kids are 9 and 5 and the 5 year old doesn't love Epcot yet). So if you have Sat- Wed as park days, you can get a lot done, especially if you go at a quieter time. You won't get everything done or even close, but you can get a lot done.
If your kids are too little to ride many rides or are not interested in the bigger rides (Splash Mountain, Space Mountain, Expedition Everest, Tower of Terror, RnR), you can save some time because those lines can be long. However, with younger kids, you have to be prepared to ride Pooh and Peter Pan 27 times in four days, ride the Carousel until your DD can be on Cinderella's horse, check out Mickey and Minnie's house, get autographs from the princesses, etc. Those can all take more time than you anticipate.
I agree with the Unofficial Guide recommendation. Even if you don't follow the touring plans exactly, there are lots of useful tips, like ride Dumbo first even if the line looks long - it grows exponentially throughout the day.
Best tips I have to maximize your time:
- stay onsite and take advantage of morning Extra Magic Hours
- get to the parks early everyday (by opening time if not before - you can get so much more done in the first few hours)
- consider a Park Hopper (about $50 more per person) so you can keep going on days when you finish a park early
- consider booking a character meal if there is someone your kids HAVE to get hugs and pictures with - they take time, but it isn't more time than eating a meal and hunting that character down for autographs, and it is a nice break
- ride Dumbo first if you are going to ride it at all
- use Fastpass. Get a FP for Pooh or Peter Pan while you are in line for Dumbo, for example
- go when it is less busy, even if you take your kids out of school (if that is an option for you)
- resign yourself to the fact that you will not get it all done and have each person pick a few attractions per park that are must-do's
- plan to come back soon!
There are probably a lot more time-saving tips that others will contribute, but this is what comes to mind right now. Happy planning!