Hi Stephanie!
If your schedule allows, I highly suggest visiting all four parks during your first Walt Disney World vacation. Each park is unique with it's own theme. If you are limited, my first choice for younger children is the Magic Kingdom. This park has the most attractions for the little ones and to me it encompasses what Disney is all about: magic and fairy-tales.
The next park my children would choose is Animal Kingdom, also my second favorite. There is so much to see and do here and we love
The Boneyard, which is a huge playground for the kids to run around in. It's nice to have a place where they can run wild and get some energy out in between the lines. Your 4 year old will have fun becoming a
Wilderness Explorer earning wildlife badges throughout the park.
If you are just getting started, check out the
Attractions page for Walt Disney World. You can filter by park and by height. This way, you can see which park has the most attractions that your family would be interested in. This is my favorite planning tool to use with my kids, ages 2 and 5. You will probably want to focus on the rides that say "Any Height" for your 22 month old.
Stop back by with any questions. We're here to help!
Have a magical day!
Leslie