Hi Justin,
Personally my children loved all four Walt Disney World theme parks when they were preschoolers and they still love them all now that they are older. However Magic Kingdom has the most attractions overall and is the one theme park I always recommend as a "Must-Do" to Guests who are visiting with children. You might find the following link for
Attractions in Magic Kingdom for Any Height helpful when planning your visit with your son. In the above linked page I have pre-set the location as Magic Kingdom and "any height" as the filter, however you can change locations or use more filters such as thrill level, interests, and accessibility.
As a Mom of four kiddos I have visited Walt Disney World since my children were toddlers and personally believe there is no such thing as "too early" for a first visit. As parents we celebrate our children's 1st birthday even though they probably will not remember the details. But as our children grow up they do remember the feelings of being loved as toddlers and they will cherish the photos you take of them during these precious life moments. Here is a link to another page for
Planning for Pre-School Kids and located in this link you will see there is a downloadable guide for
Pre-School Parent's Guide to Walt Disney World as well as other helpful information and videos. Finally my last piece of advice is to let you know that children under the age of 3 are considered Guests of Mickey Mouse himself and are free to enter the theme parks!
Thank you for stopping by the Disney Parks Moms Panel with your question Justin. Please let us know if we can help answer any further Disney vacation planning questions.
Blessings,
Brenda