Hi Bridget!
I love your Walt Disney World Resort vacation plan already.
Disney's Art of Animation Resort is amazing and I am certain you and your son will both love it!
If I were choosing between the dates you listed, I would go with the week in May for a couple reasons. Most schools will be out for summer by the middle of June and I always try to visit Disney Parks during the regular school season if possible to cut down on crowds and costs. It's likely that you will see heavier crowds at the beginning of your trip over Memorial Day, but there are also some great deals to be had.
I checked the
Special Offers on the Walt Disney World Resort website and there are a few offers available for dates in May that might be just right for you.
As for the weather, there isn't much of a difference in the averages during the months of May and June. That said, I think you'll have a better shot at milder weather if you travel in May.
No matter what you choose, I know you will make magical memories with your son. Thank you for visiting the Disney Parks Moms Panel, Bridget. Hope to see you real soon!
Andrea U.