Hi April!
Thank you for bringing your question to the Disney Parks Moms Panel!
Generally, early to mid-May is a great time to visit
Walt Disney World. Most schools are still in session, so the crowds are lighter and the weather isn't quite as hot as during the summer months. We have visited in May on several occasions and always had a great time!
I like to look at the crowd predicting website, Touring Plans, when choosing a time to visit. They are predicting the crowds that week to be between a three and five, with ten being the highest. That's a great level. Obviously, these are just predictions, but they tend to be pretty close with their numbers.
I hope this helps! Please let me know if you have any other questions.