Kristy,
This is EXACTLY the situation my family faced last year. Here is what we did.
We left our hotel (on the monorail line, but your plan could still work) and made our way to the Magic Kingdom. Then we took the boat from in front of the park to Fort Wilderness. We scheduled it to be there an hour before check-in time. In your case the bus ride to the Magic Kingdom, followed by the boat, is the easiest route from resort to dinner that you can follow.
Once there we went to the
Tri-Circle-D Ranch. It is immediately next to Pioneer Hall, so we were not worried about having to trek back to the restaurant. We toured the stables to look at the horses that are used in the Magic Kingdom park for many different carriages and ride vehicles. The stables are immaculate, and the tackle and other exhibits are very interesting. After that our girls went on pony rides, which was very well done also.
That could have taken us the whole hour, but we also got to log some playground time in (which is also right there) and just generally explore the area. There is a small store which has some interesting items too.
Finally, if horses are not your thing, you could also consider renting a boat from their marina. Time dependent, that could be a fun alternative.
BOTTOM LINE: For earlier dinner times like yours, I think this is the easiest, most scenic route available. I also think that either horses or boats seem to captivate most kids.
Write me back if there is some other kind of experience you would like to seek out between your Animal Kingdom and Hoop Dee Doo experiences.
Have a magical vacation!