Hi, Kelly! You are certainly going to have a lot of fun with all of those kids! It sounds like a great vacation is shaping up!
For the most part, at least where my family is concerned, after spending a long day in the theme parks, then having dinner, my girls are ready to call it a day. I usually get back to the hotel, get everyone showered and in pajamas, and they watch a little television before turning in for the night.
If you find your gang still has energy to burn, you could take them all down to the pool or to the playground at your resort for them to swim and play a while. Another option is shopping at Downtown Disney, with some time in the Lego Playground for the smaller ones. How about an evening game of miniature golf?
I think you may find, though, especially with the heat and humidity, they might be ready for bed not much longer after you leave the theme parks. And if not, get them up earlier the next morning for the Extra Magic Hours! That will help them fall asleep sooner that night!
One other option for some of the kids might also be one of the Kids Clubs on property. You'll find them at several of the resorts, including the Polynesian and Animal Kingdom Lodge, and they offer babysitting services that the kids will love. There are activities, food, and fun for kids ages 3 to 12 (they must be potty trained). This gives the grown ups a little time to themselves as well.
Have a terrific vacation!