Hi Dianna!
Welcome back to the Disney Parks Moms Panel. I have ran during the
Disney Princess Half Marathon Weekend a handful of times and I'm glad to tell you I don't think the marathon will have an impact on your trip!
Saturday, February 25th is the Disney Enchanted 10K which will start and end near
Epcot and will likely conclude before that park opens for the day. Sunday, February 26th is the Disney Princess Half Marathon where the end of the course runs through
Future World inside of Epcot.
In my past experience, most marathon runners will head to
Magic Kingdom or remain at Epcot. Otherwise, I think you'll find the schedule and park crowds relatively unaffected.
I hope you have a magical trip and please let me know if there is anything else we can help you with!
-Lindsey