Hi Michelle! I'm sorry you weren't able to secure an Advanced Dining Reservation at Garden Grill...but I wouldn't give up hope just yet. Keep checking daily, preferably first thing in the morning, to see if any cancellations have come through or more availability. You just never know, and you might get lucky.
That said, if you are unable to, or want to have a backup plan, one of my family's favorites is
Teppan Edo in Japan. It is a Japanese steakhouse, similar to Benihana if you have those near you. Even though there aren't any Disney characters there, you really do still get a show with your meal in the form of the chef cooking right before your eyes. The other reason my family loves it is my picky eaters (and my non-picky eater) always have things they'll enjoy there. My oldest has always loved getting steak there since he was old enough to eat it. My littlest one, now 2.5, will eat white rice if nothing else. My adventurous daughter fell in love with everything there from the salad to the main course and perfected her chopstick use as well!
Another choice might be the
Coral Reef restaurant, located inside the Seas pavilion in Future World. The 'show' here is the gigantic tank filled with tropical fish, sharks and sea turtles that swim right before your eyes as you dine. Here you will find delicious seafood and other specialties as well as a regular kids menu. We always have a great experience there as well.
I hope that helps with your dining decisions and that you have a wonderful time on your vacation!