Here are my quick thoughts on the three days you have in Disney...
Most every family spends a full day at the MK - there are a ton of things to do there.
Between the last three parks...there are LOTS of things to do - more than any family could do in one trip...so each family has to make a list of the things that would appeal to each...
For me...here are the must dos at the other three parks:
Epcot:
World Showcase - I would skip this if I only had three days with kids...unless my kids were excited about the countries. Not that it isn't great - there are fun things there to do - but not anything a family can't live without, in my opinion.
Future World - Must Do's, in my opinion:
Wish Lounges - there are at least 2 in Epcot - your wish trip will be the ONLY time you get to see these...so go for it!
Soarin' - if your kids are tall enough and not afraid of heights - best ride in Disney.
Turtle Talk with crush - I love this, especially for little kids that would "talk" to Crush.
GREAT place to see a BUNCH of hard to find characters - use the button and see them all!
Animal Kingdom:
Safari seems like a must do - but I could skip it. Like driving through a zoo...unless that is your thing.
Expedition Everest - great roller coaster - not TOO terribly fast, does go backwards.
Lion King - MUST DO show! Show them your BUTTON - sit toward the front!
Finding Nemo Show - MUST DO show! Sit in the BACK section on the FRONT row...best seats in the house! Try NOT to sit in the front section...The whole point of the show is that these puppets are being worked by humans and if you sit too close, you can see the "humans" and miss what the puppets are doing (which are supposed to be the focus)...being so close tends to ruin the magic for me for this particular show.
DHS:
This is a harder park...as it depends a lot on YOUR family and their interests...
Toy Story is a must for everyone! But other than that...each attraction stands on its own...to do everything would really take all day - and maybe two if you only do parts of days...
anyway...I am sure you didn't want THIS much info...but that was on my brain tonight!