Hi Hollie!
It sounds like your husband has had an amazing running career and I love that y'all want to do a
runDisney race together to commemorate your birthday! There are 4 different running weekends at Walt Disney World Resort that I think will have a variety of pros/cons for y'all when traveling.
Walt Disney World Marathon Weekend- Since your Hubby has ran the Goofy Challenge y'all are probably already familiar with what this weekend is all about. This is the largest of all runDisney weekends and probably caters most to veteran runners like yourself. The one negative to this weekend can be the weather, which can be tricky when traveling with a toddler. If you are used to cold weather, it will probably feel like a break, but for this Texan it's chilly. With that being said, I'll be doing the Dopey Challenge in 2018 with a toddler in tow!
Disney Princess Half Marathon Weekend- This is personally my favorite weekend, I think mostly because it was my first! Since you'll be celebrating your big day, I think doing a Princess run is perfect for you to receive the royal treatment you deserve. I have ran this race in 30 degree and in 80 degree weather, so unpredictable, but that's Florida!
Star Wars Half Marathon Weekend- The Dark Side- If y'all are Star Wars fans this is the weekend for you! Weather wise, I think this is the most ideal weekend, and of all the races I think you'll also find the lowest crowds in the parks.
Disney Wine & Dine Half Marathon Weekend- What's great about this run weekend is you can usually catch the end of fall decorations, the beginning touches of holiday cheer and the weather is mild. The draw for many runners to this event is the Post-Race Party though, which may be too late for you to enjoy with a toddler!
Logistics wise I don't think you'll see a large variability for the ease of traveling with a little one.
-Lindsey ºOº