Hi Kristina!
Welcome back to the Disney Parks Moms Panel. I bet your little ones look positively regal in their Tiana and Elena dresses and I don't blame them for wanting to show them off!
One of my favorite things about all runDisney events, and specifically
Disney Princess Half Marathon Weekend, is the costumes and get-ups you'll see on runners! While I understand it's not for everyone, for me it's a large part of the fun. As long as they are able to safely run in them, your kiddos can absolutely run in their Princess dresses. You'll find it's a pretty even split between children that wear a character costume and those that wear plain clothing, so it's certainly a fitting time for them to rock their dresses!
The rules that Disney enforces with regards to children costumes is that they don't have any toy weapons or masks that cover their entire face, but that doesn't seem like a concern for Princess Tiana or Elena of Avalor. This
runDisney blog post outlines the full runDisney Costume Guidelines if you'd like further clarification.
I hope your Princesses receive the royal treatment during their runDisney Kids Race! Please let me know if you have any other questions and I hope y'all have a magical time.
-Lindsey