Hi JBAAR Family. Sorry if this is repeat info, but if you haven't ever been to Disney, you might want to do some reading up on what time of year to go, thinking in terms of crowds. Those are great ages for kids to go -- any age really is great -- but each child may have certain attractions he or she really wants to see because of their various developmental interests, so your planning might be a little more involved than a fam with say, two close-aged teens or a single preschooler. Lower crowds = more time for fun, so you might be able to fit in more for everyone in your party.
We've been there twice -- Trip 1, my older son had just turned 4 -- he remembers the big highlights. My younger son was 6 months and it was unbelievably easy to navigate parks and rides with him! Trip 2 was last Oct.; they were 8 and 4.5. Loved it, talk about it all the time, know every park and attraction by heart. My younger one never did nap that trip, but did tire out by 8 pm or so.
No matter how old they are when you eventually go, half the fun (and family togetherness) is in the anticipation. Try a countdown on a calendar (we made a paper chain from Disney scrapbook sheets for the last 30 days and the boys took turns ripping off a link each day), family movie night to re-watch all the favorites and some you've never seen, get the park maps and go "exploring." Make a list of Disney trivia for the trip. Make wish lists for attractions and touring plans, but always keep flexibility at the forefront -- so no broken hearts if Haunted Mansion happens to close that day or the line for Pocahontas is just too crazy long.
Hope that isn't too far off-topic. Good luck!