please, by all means, don't skip Epcot! make it a half day thing if you have to, but don't skip it altogether. really, the enjoyment level of the park according to kids just depends on the kid. my sister and i loved the place when we were little, but i was 8 or 9 at the time, so that could have had a little to do with it. there is an attraction there with dinosaurs (Universe of Energy) if your boy likes them, there's a thrill ride in a test car (Test Track, though i'm not sure if 4-year-olds usually meet the height restrictions) if your boy likes cars (you could at least take him in the gift shop), there's a thrill ride where you go into space (Mission: Space, the newest WDW thrill ride, though, again, not sure about the height restrictions) if your boy likes space (again, you could at least take him to the gift shop, and there is a game area just past the shop). Innoventions is a great place for kids to play with technology (and they do have kid-friendly technology there...after all, it IS Disney World). there's Journey Into Imagination where you take a trip through an imagination 'lab'...it's a fair attraction, though we 'Disney-vets' tend to compare it to the excellent original version. then there's the Living Seas, which is an outdated two story aquarium...but i doubt a four year old would recognize the outdatedness...live animals usually attract childrens' attention more-so than architecture (BUT Living Seas is scheduled to shut down for a refurb sometime in March, so i'm really not sure if it will be open by the time you go)
really, there's a lot more for boys to do in Epcot than girls (unless they're tom-boys like i was/am) so you have an advantage there. now, usually adults like World Showcase more than kids, BUT they do have passports and kid cots in every country, which makes things a little more interesting for the kids. passports are little kits which include a booklet, stickers, and maybe even a button (they used to have buttons, not sure if they still do) you take the passports to a designated area in every country, and someone native to that particular country will write a greeting in their native language, tell you what it says, and stamp the passport. it really makes a great souvineer! kid cots are tables set up in every country (well, used to be every country...not sure if it still is...you may have to ask for locations) every table used to have something different to make (crafty things) but i think now they all make masks. i wish i knew more about kid cots, but i was 15/16 when they started them in 1999/2000, so i've never stopped at them.
and polyman's right. don't get in so much of a rush that you forget to stop and take in the surroundings. that's one of the things that makes Disney really unique! it's great that you've been reading up on the World! that'll give you kind of an idea of what you and your family want to do. if you haven't already, i would suggest making a list of 'must-do's'. and try to be realistic...if you're 'must-do' list includes the word 'everything', you might want to narrow it down a bit :animwink:

you might even divide the list into 'must-do's', 'want-to-do's', and 'like-to-do's', and include attractions, dining, and shops. just a thought
also, not sure if anyone on here has mentioned this, or if you know already, but people staying on Disney property has the advantage of Disney transporation. Disney buses take you from your resort to any Disney theme/water park, and Downtown Disney. and there's a monorail between Epcot and Magic Kingdom. since you're a first-timer, definately take a monorail ride at least once! even if you're just taking a roundtrip around the Magic Kingdom resorts, it's something you should experience!
i'm not sure how long you're staying at WDW, but since you have a little one, my bet is that you'll be spending the majority of the time at Magic Kingdom. the other three parks (especially MGM, and maybe even Animal Kingdom) are probably half-day parks in your case (then again, they may not be). so plan at least 2 days for MK, if you can spare them. when it comes down to it though, you can NEVER have the perfect plan for Disney...usually you just gotta play it by ear, especailly if your a first-timer. plan as much as you can, but keep your options open and flexible. you may get down there and decide you'd rather spend more time at AK than MGM, or more time at Epcot than AK. you can listen to our suggestions as much as you want, but remember they are JUST suggestions. it all really comes down to you and your family and what you like to do, and what you expect out of your trip.
oh, and just to warn you, if you're not used to a LOT of leg excercise, WDW consists of a LOT of walking, so take super comfortable shoes (new shoes usually don't cut it unless they're warn in pretty good)
my brain's all out of good WDW first-timer tips for the moment. i may have more later :animwink:
have a magical trip!!! :wave: