Hi Gwen!
Thanks for your question and for visiting the Disney Parks Moms Panel!!
Boy, have you asked the $64,000 question!!! In years past, and before the addition of so many other recreational activities and events around
Walt Disney World Resort, there were very specific "seasons" as Disney liked to call them. There was a "holiday", "peak", "moderate" and "value" season and they were specifically "dated" and made planning WAY more easy if you were trying to avoid crowds. That said, with the continuous theme park expansions, new resorts,
Disney Springs expansion,
ESPN Wide World of Sports and
runDisney events, you kind of get the idea that there is almost ALWAYS something going on around the World!
There are still some somewhat slower times of year to try to plan to come, however, such as...the second half of August (school is starting back up most places in the U.S.A.), most days in September and most weekdays in October, most of November minus Thanksgiving Week, and most especially, and my FAVORITE time to visit, the days between Thanksgiving and Christmas.
I hope this helps and I wish you a magical trip whenever you may come!!
Chris