Hi Karen,
Welcome to the Disney Parks Moms Panel. I also have three children, so I think I can help with your question.
Many of the attractions at Walt Disney World Resort will seat five Guests all together, especially since your girls are so young. You will easily be able to sit together on things like
Pirates of the Caribbean,
"it's a small world", and the
Jungle Cruise for instance. There will also be many attractions where you can split into two groups like
Peter Pan's Flight,
The Many Adventures of Winnie the Pooh, and
Dumbo the Flying Elephant. For interactive attractions like
Buzz Lightyear's Space Ranger Spin, I usually ride with two of my children and let them play the game while I help.
For any attractions that you are unable to all ride together, just ask the Cast Member about the
rider switch service. This will allow one adult to wait while the other adult takes a child on the attraction and then switch places without having to wait in the regular line again.
I hope this helps to ease your mind about your upcoming vacation. One way or another, everyone will get to enjoy all of the attractions. Have fun and make some magical memories!
~Carrie