First try to be at the park before opening about 20 minutes or so so you are in line to be some of the first to get in. This will help reduce your wait times.
With kids your age I would recommend using FP in this order (you also need to check height restrictions for that 4yr old).
MK
Big Thunder
Splash
Space Mountain
Buzz Lightyear
Peter Pan
Pooh
Jungle Cruise
Stitch (I'd skip this one for the 4yr old its scary and maybe the 7yr old unless they are not frightened of the dark and aliens)
Philharmagic
Epcot
Soarin
Test Track
Mission Space
Maelstrom (Norway, in World Showcase)
Living with the Land
Honey I Shrunk the Audience
DHS
Toy Story Mania (FP will run out early in the day and lines swell easily to over an hour)
Rock N Rollar Coaster
Tower of Terror
Star Tours
Voyage of the Little Mermaid
Animal Kingdom
Kilamanjaro Safari
Expedition to Everst
Kali River Rapids
Primeval Whirl
Dinosaur (again I'd have the 4yr old sit this one out, and maybe the 7 yr old)
It's Tough to Be a Bug (this one is scary to many little ones as well)
geeen-often not needed FP's and machines may not be running. General rule is if line is less than 20 min standby don't use FP.
Hope this helps.