Welcome to the Disney Parks Moms Panel, Anna!
I am here to help offer a bit of clarification so you may enjoy your time with your family at your
Walt Disney World® Resort hotel pool, or the Water Parks; my family loves our pool time.
With regard to "diaper aged children" being required to wear swim diapers while in the pools, they are referencing those children who are not yet independently toilet-trained. Any of your children that wear a diaper on a daily basis and cannot use the toilet as their method of release, will require a swim diaper.
I hope this helps, Anna! I'd love to know where you are staying - I can offer advice on all the fun activities available at your Resort's pool, or at any of Walt Disney World's Water Parks. Many offer splash pads and kiddie pools for younger tots.
I'm just a swim away and hope to hear from you again!
Faith