Hi Natalie!
I don't think you are crazy at all! Disney World is THE place for kids, so I am sure they would love it!
If you are worried about crowds, they are actually very mild during marathon weekend. If you are a runner, it seems like there are runners everywhere, but actually park levels are very low that weekend.
You didn't indicate whether you or your husband plan to run, but if someone is, it really isn't that difficult either. What we generally do, if I am the only one running, is my husband sleeps in with the boys. They get on the Disney bus that will take them to the race, and they meet me at the finish line! Sometimes they like to go to Magic Kingdom to watch me come down Main Street, but they generally just meet me at the end. There will be buses to and from all race weekend events available at all Disney resorts that weekend.
If you are wanting to cheer someone on, check out the
chEAR squad packages. These are great ways to have priority seating at different areas. You can find the information at that link, just click on "event overview" and then "chEAR squad".
Please let me know if you have any other questions!