Hi Tara!!
Don't you just LOVE planning your next Disney vacation?! It is so much fun!
I have been to Disney with my family in mid May and in October. From my experience, the crowds were better in October than they were in May. I also recommend going in October over May because your family will have the opportunity to experience
Mickey's Not So Scary Halloween Party! My five kids (age range from 11 to 2) absolutely LOVE this special event, and so do their parents! If your schedule is flexible, try to plan your vacation in early October. The closer you get to Halloween, the crowds will increase.
Another reason why I would recommend going in October 2013 is
because of the Fantasyland Expansion. While Disney World does not publish any firm dates, it looks like the New Fantasyland Expansion will begin opening in phases starting early 2012 and continue through 2013. From everything I have read, the later you go in 2013, the more your family will be able to experience in the new and MAGICAL Fantasyland!!!
I hope this helps you in your planning! If you have other questions, please let us know!
Have a MAGICAL day!
Wes