Hi Lizzy!
Thank you for bringing your question to the Disney Parks Moms Panel. It was through
runDisney that my obsession with visiting the Disney Parks truly began and I'm so excited for you and your husband to experience every magical mile along the way!
While there isn't a direct service provided by Walt Disney World Resort, I know many people that have utilized the third party service,
Kid's Nite Out, with great success! They'll send a caregiver directly to your room in the wee hours of the morning so you and your husband can run the half marathon and have peace in knowing your little mouseketeer is being watched back in the comfort of your room. For runDisney weekends, they do tend to book up rather quickly though as many parents are in a similar situation to yours. I'd make sure to call them as soon as possible so you know everything is taken care of before you arrive! To contact Kid's Nite Out, please call 407-828-0920 any day from 8 AM to 9 PM.
I hope this helps to plan your runcation early next year! Please stop by again if we can help in any other way.
-Lindsey