I think 4 is a great age to take the kids. You may be surprised to find how much your kids will enjoy the autograph signings. In case you don't know, there are several designated areas in each park for character signing (grouped by themes [Mickey; Winnie the pooh; Frozen, etc...]). I will never forget the sheer joy on my 4-year-old's face when she was getting autographs from Mickey and the gang. I would plan some time for that each day.
Number one tip: go early (rope drop). You will get more done before 11 than you could get done the rest of they day. I recommend planning your day by going early, ride several of the rides early while the line is short, then by mid-late morning, have some fast passes to finish that part of the day. We really loosen up on ice cream, popcorn and sodas during this part of the day... it seems to keep the kids "in the game" better. Then maybe break for lunch or to go to the hotel's pool for a bit. This break is huge. Even a 4 year old that doesn't still nap may need a nap and will certainly need a break from the overstimulation. Getting to the resort to decompress and grab some food for a few hours really makes the trip more enjoyable. Then you can go back in the evening for to enjoy the park at a more leisurely pace knowing you've already ridden most of the good stuff. End the night with the firework show and I'd say your family would have had a successful day.
consider using an official Disney travel agent. They are free and can help you with a lot of information that you might not know if you aren't real familiar with Disney.
use tourplanning.com; it is 12 dollars and well worth it. You will get it free if you use an official Disney travel agent. mapping out the activities to do is very helpful. They help do it in a way that makes sense so you aren't walking back and forth across the park too much. That can be a time killer. If nothing else, make a tour plan for the magic kingdom. There is so many rides there you will never get to do everything without a plan.
If you can afford it, the Contemporary is great for families with kids this age. The biggest advantage in my mind is being able to walk to and form the Magic kingdom. You will be absolutely amazed at how stressful some parts of your day there can be. In a very short period of time it seems your kids (maybe an adult ; ) just hits the end and needs a break. This is most likely at the Magic Kingdom. It is great but can be overwhelming if you try to take it all in at once without a break. Having the option to just take a 5-10 min walk to your room is sooo much nicer than fighting the lines for a bus when you're group is hangry. This in my mind is what sets the Contemporary apart from all other resorts. Even the other monorail resorts. Sometimes the line for the monorail is long or there simply isn't a train there and you may wait a while, then you have to make 2, 3 or 4 stops to get to your hotel. This makes the Contemporary worth more money.
Everyone is going to have a lot of opinions about a park you can skip. I've read several that say to skip Hollywood. I would suggest you go to all 4 on your first trip. I personally love Hollywood. And even though your kids will not ride the two big rides (that are currently) available there (Tower of terror and Rockin rollercoaster), it is still well worth it for our family. Toy story is possibly the best ride in all of WDW for kids that age. There is also several shows that 4 year olds will love (Frozen, Ariel, Beauty and the Beast and Disney Junior, I mean come on!). And if you personally like roller coasters, then jump in the single riders line for Rockin Roller coaster. My wife and I would do that until our kids could ride it. WHile one rode, the other just sat with them for icecream. Single riders only takes a few minutes.
You walk A LOT! My kids are very active so I couldn't understand why they were lagging behind by the end of the day (especially EPCOT). Well, its pretty simple, we walked close to 14 miles each day! Even with 4 year olds, you may not want to rule out renting a stroller. They have them for a few bucks at the entrance of each park. They are made for older kids and could come in handy if you notice them getting really tired. They are easy to just jump in and out of too (they aren't really strollers in a traditional sense, more like a rolling platform with shade.
At 4 I would plan on being at the park when it opens. We use the beginning of the day to get our rides done (with fast passes for later morning/early afternoon). At MK we usually stay to watch the parade at 2 and then head back to our hotel. Then we relax, maybe swim, maybe a quick nap, or a beer, whatever. We may have an early character dinner (1900 park fare is a good one for girls) then head back to a park for a couple of rides with short lines; or just to walk around and enjoy the place. We put very little pressure on ourselves to "do things" in the evening. We may do some of the less popular or fairly quick things at this part of the day but we don't kill ourselves in long lines at this time (things like Magic Kingdom's Tiki room, Ariel's ride, small world, mickey's philharmagic, the laugh floor, etc...) We then find a good place to watch the fireworks.
Each park has an evening show. In all the times I've gone, Ive never stayed for the animal kingdom show. I haven't heard good things. And, like I said before, people have different opinions about parks; mine is that AK is my least favorite. We love the Magic Kingdom show. The show there was updated this year and now it is more important to have a view of the entire castle. Before it was mainly a firework show up in the sky. Now that isn't the case. You will need to have a good view of the caste or you will need to find a way to hold two 4 year olds on your shoulder so they can see.
I personally love the show at Epcot. You can see it from anywhere around the lake (in the center of the world showcase), so it never feels quite as crowded as magic kingdom. Granted, it is not quite as entertaining as MK's show, and it is a bit dated, but I still love it. Personally I find it to be more accommodating night. You can go find a place (I like the benches in Germany) and sit there before the show starts. We like to get those big german pretzels for everyone to share and my wife and I get a couple of beers and just relax and wait for the show.
Ok, If you possibly made it this far. You first need to decide when to go. since your kids aren't in school, you should REALLY think about not going during peak times (spring break, Chirstmas) and don't go when it is too hot (pretty much don't go July through Sept, june is probably not good either). Then Where to stay. Ive been too many times, but I'm convinced there is no perfect place. The monorail parks are probably the closest to perfect. I think the contemporary is the best of those. Second to the monorail parks are the ones behind Epcot (Boardwalk area). Then decide on meal plan or not and book your character meals. There are a lot of popular meals that you will need to book on the first day you can (Be our guest; cinderella, chef mickey) and some that don't go quite as fast (1900 park fare). Then come up with an itinerary for where you will be each day. I would suggest giving some preference to the park that has the EARLY morning extra magic hours. I personally don't find any value in the parks that stay open late, especially with 4 year olds. Once you know where you will be, make a plan on touring plans. Then when your are first able to, make fast passes for what tourplans suggest. I personally would suggest late morning fast passes. You should be able to ride some of the popular rides fairly quickly first thing in the morning and not have to use a fast pass then. It would be a waste to use a fast pass for Peter pan, or toy story at 9 am when you could have gotten on the ride in 15 minutes wait time at 9 am anyway. use that time of day to ride the things you didn't get fast-passes for.
Lastly, all the parks serve alcohol except Magic Kingdom... Plan accordingly
ok, I'm done... for now ; )
