Hi Rachael! Thanks so much for bringing your question to the Disney Parks Moms Panel!
Rachael, a mini trike would be considered a type of bicycle, and
property rules state that bicycles are only permitted in designated resort areas, so, unfortunately, you would not be able to use it in lieu of a traditional stroller or push chair.
If you would like something smaller, I would suggest bringing an umbrella stroller, as those should easily conform to the stroller size limits of 31 inches wide by 52 inches long. An umbrella stroller will also be quick and easy to fold up to hop on and off of transportation and is relatively lightweight. If your little one will be in the stroller more often or is planning to nap on the go, you may find it worth it to bring a traditional stroller.
When deciding which stroller to bring, please make sure you are familiar with the
stroller guidelines, which state that strollers must fit within the above-mentioned size guidelines and must be a push-type stroller as opposed to a wagon-type stroller.
I hope that this gave you some clarity on the guidelines, Rachael, and please come back to the Disney Parks Moms Panel if we can help as you plan your magical holiday!
Sarah B.