Hi, Jason!
Welcome to the Disney Parks Moms Panel and thanks for your question! You’re going to have a wonderful trip to Walt Disney World with your princesses.
There are lots of attractions your youngest daughter will be able to ride, especially in Magic Kingdom Park. If there’s no minimum height requirement posted at an attraction, she can definitely ride it. You can also check out the interactive attractions list online to see exactly what your 3-year-old is tall enough ride. I think you’ll be pleasantly surprised by just how much the whole family will be able to experience together!
I’ve been taking my son to the theme parks since he was just a few months old. When he was an infant, I often used a baby carrier and would even leave him strapped to my chest for the ride if possible, which meant my hands were free to take pictures and point out characters to him. It also made entering and exiting the attraction easier.
Keep in mind that Guests with children who don’t meet the minimum height requirement may take turns experiencing attractions using the Rider Switch program. It allows an adult (and older children) to ride while another adult waits with younger children. You then "switch" so the second adult can enjoy the attraction without waiting all over again. The specific procedure can vary depending on the attraction, though, so it’s best to let a Cast Member at the beginning of the queue know you’d like to use Rider Switch and ask what steps you should follow.
I hope this helps, Jason, and that you have a wonderfully pixie-dusted vacation to the Walt Disney World Resort! Please write back with any other questions you may have as you continue to plan.
Wishing you magic,
Courtney