You asked here, so you will mostly get the standard line. 1 day at least per park. Park hop. 2 days for MK and maybe 2 for Epcot, a down day (or 2). But that makes for a LONG trip and tired little feet. Is this your first trip? Will you be going back?
After 2 or 3 long family vacations fighting tooth and nail to find the magic that we loved before we had kids, I think DH and I have finally pegged it. We are there for VACATION. I could go-go-go for 7 days straight, but it doesn't work for DH and the kids. PH never proves to be a value for us. We always wish we'd spent more time enjoying that fabulous hotel we paid good money to sleep in. And we always get too tired to do everything we wanted to do.
So last trip we pared it down to a long weekend. Only visited MK and remembered that we could upgrade tickets and add park hopping up to the last day of my ticket. I know myself well enough to know if I plan extra parks and the hopping, then I will expect everyone to stick to the plan. Instead, we had arrival day at the resort and to tour around the monorail hotels (dining, shopping, our pool), 1 day at MK with a 3 hour break for early dinner, and a day at Fort Wilderness (only cost was food we ate and DD's trail ride). We spent less money and left already planning what the kids want to see at Epcot.
Don't underestimate all the other things you can do to fill time. Disney Springs, mini golf, water parks, just exploring, a resort character meal . . .
This trip we'll do Epcot and AK and resort time. I'm adding in HS for Star Wars against my better judgement.
Will your kids enjoy all 4 parks more than you expect? Yes.
Will you need more time no matter how much you cram in? Yes.
Will you run out of things to do? No.
Will you get mileage out of a park hopper? Maybe
Will your kids hit a wall and your plan go out the window if you try to do too much? Probably, especially if this is your first trip.
Know your kids, ask their opinion, and resist the temptation to do it all. Ask them to tell you 1 or 2 things they've heard about that are really important to them. They might surprise you.
Trying to keep up with the rest of the wonderful DISers just isn't always what's best.