Itinerary
I would also second avoiding DisneyQuest (and Downtown Disney) with your limited time and children's ages. Maybe when they are in their early teens and have seen a lot of what else the park has to offer.
You didn't say where you are staying which can have some impact on your visit. Staying on site can have an entertainment value of its own, and also changes your flexibility and approach to travel. In either case, your kids are still young, so I would suggest you plan your days with breaks in the middle and I would urge you to plan to take advantage of strollers (your back and the kids will thank you by the end of the day). You also didn't indicate what time of year you're going or what you did see the first time around. All that info could help with suggestions.
Don't know what all you covered in your first trip, but here are some thoughts (for what they're worth)
The children should be old enough to enjoy the parades (AK, MGM, MK), fireworks (Epcot, MK). Fantasmic may be too intense at this time, but if you do go, use a dinner package to limit your sit/wait time.
Check back on the Disney site or Allearsnet.com for seasonal specials (Christmas, Halloween, Flower and Garden, Food and Wine Festival etc.)
Hoop de do Review dinner show is always a lot of fun, and often overlooked by newer visitors. The show at Polynesian is also nice, but less so for younger ones. I wouldn't suggest the other shows.
There are shows in all the parks that you may have missed the first time around that are good to plan for. In AK, you have Lion King and Tarzan which are fun, high energy and not threatening. Epcot has a lot of street performances to enjoy. I would plan on one meal for a character visit. There are different sites that tend to have different characters, so plan to your or the kids favorites at this time. With that said, many kids are scared of the characters in person...they are BIG. Possibly judge with street contact before spending the extra money on the meal.
I have found that those ages are particularly hard to prejudge what children would like. Some rides you never expect scare the heck out of them while others you don't think you should do, they love. Yes, unfortunately Small World is closed for rehab. (You can check the Disney website for lists of closings/planned closings) Buzz Lightyear would be fun for all as are the simple things like riding the horse drawn trolley and the train. You may want to check out Mickey's Toontown for that age group. Instead of IaSW (Small World), you can substitue Rio de Tiempo in Mexico (Epcot). Space Ship Earth, Living Seas, Journey to Imagination, The Land and Universe of Energy are all good for that age group (and all age groups!)
MGM had some shows for younger ones to the left of "the hat" as well as the Muppet show and a Honey I Shrunk...play area. Characters around MGM will probably have a lot of appeal.
I'm sure you'll get many more suggestions, just do SOME advance planning, ID a few must do's for the day but otherwise slow down and enjoy at their pace. Water parks are nice for the middle of the trip as it allows for a lower energy relaxing day. Again look at AllEarsNet.com for a great meal planning resource.
Report back to us how you make out.