Hi Anne,
Thanks for stopping by to get our opinions and suggestions to help guide you in your planning process. Your kids' ages are perfect for this park as many children that age adore all kinds of animals and Disney's Animal Kingdom is the perfect place to see the animals interacting in their natural habitats, while also experiencing some Disney magic.
In the many times I have gone with my little ones those ages, we have been able to do the park in a day. There are several attractions that they may not be tall enough to ride, so that takes time spent on those rides out of play. With the rides and shows and other interactive experiences for them to try, you should easily be able to get to most of it in one day. One of my daughter's favorite things from our trip last summer was the
Wilderness Explorers. This interactive activity throughout the park is a fun way for them to see many parts of the park while also learning in the process. My daughter was 6 at the time and seemed to be at the perfect age for it. It is included in the price of admission. I strongly urge you to try it.
In regards to dining, I think your kids would enjoy Tusker House more. Sanaa is an amazing restaurant, but as you said you would need to leave the park to go and the atmosphere can seem a bit more fancy, which your young ones may or may not enjoy. That would be your call. Tusker House has a wonderful selection of choices and is conveniently located within the park.
I hope you have a magical trip!
~Allison L