How much to do and when depends on a lot of factors....the nature of your children, how crowded the parks are, how hot or rainy it is, etc. During the hottest weather when the parks are open late, we've done what dixipixi outlined in her message. However, we've also varied things a bit by not always getting an early start in the morning, by staying in the park most of the day and returning to resort at night for dinner, etc. It's very difficult to plan when you don't know how your party members will react. And with children, sometimes how they react changes from trip to trip!
That being said, one of the key things we've learned and try to build in is flexibility. Structure a touring plan around your "must sees" (and no, it can't be everything!). If seeing SpectroMagic and Wishes in MK are important, then you've got to manage your children during the day so they don't meltdown at night. That may entail doing a park early in the morning, returning to your resort in the afternoon for a swim and a nap, and then going to the MK. Or it might mean sleeping in that morning and beginning your tour of the MK around 4, when the PM parade has ended and lots of folks are exiting the parks with their tired little ones. For my family, a sleep-in morning usually always follows a late night. Epcot future world is a park that is good to start touring in the PM as most parkgoers have toured it in the AM and move on to the Future World portion for the afternoon.
Dining reservations are good if you really want to eat at a particular place at a particular time and perhaps see characters, but they can also limit you. MK, as well as the other parks, have a variety of counter service restaurants that have good food. One of the reasons why I mention this is that I hope you do not stay away from MK because you cannot get ADRs for dinner there. Nor would I want to see your flexibility constrained by a multitude of ADRs. Hope that makes sense!
Let's see, another of our tricks to increase our mileage, so to speak, with our kids is to
rent a stroller if we planned to do Epcot for an entire day. It's a lot of area to cover. Some folks have the opinion that older children should not require a stroller, and in most cases, that is true. But the walking done at WDW, especially Epcot, is beyond the norm and it helps to get a couple of extra pleasant hours out of our kids. Heck, sometimes I'd like to be pushed around in a stroller!!!
Anyway....keep reading the Disboards, keep asking questions, realize you won't get everything done, and I'm sure you'll do fine and your trip will be great.
Hope this helps!