Hi Jeri!
Oh, I like you already! How fun that you are bringing your granddaughters to Disney World! I honestly can't wait to do the same one day--my daughter is only 5 but I know it will come soon enough! :)
Anyway, yes, there IS something special going on--
Epcot's Flower & Garden Festival! There are topiaries covering the park--all in the shape of your favorite Disney characters! There's a butterfly tent, special gardens, famous gardeners (are there famous gardeners?) and lots of beautiful flowers everywhere! It is one of my very favorite times to go to Disney World.
I'm not sure how old your grandaughters are but if they are interested in Tangled, there is a semi-new meet-and-greet with Rapunzel and Flynn at the Fairytale Garden in Magic Kingdom (I hear you have to get there when the park opens so you don't wait in line so long!). And the new Disney Junior Live on Stage features the new show Jake and the Neverland Pirates! Oh, and I just heard Disney Dad Marc say the new ending to the Haunted Mansion is live!
Let me know if you have any other specific questions! I'd love to talk more! Have fun with your girls!