No worries Kim! Those of us with half a dozen in our family tend to encounter a world not quite equipped for so many kids at once. At Walt Disney World, however, your crowd can easily enjoy the rides.
Typically you will not find two seater rides. Many attractions, such as Pirates of the Caribbean, "it's a small world", and Kilimanjaro Safaris, ferry you about in a large jeep or boat and can handle your entire brood on one row. Rides with smaller conveyances will accommodate at least three. One adult can accompany two children so the kiddos are never riding on their own.
Your older children will adore
Rider Switch. This option allows your taller children to get soaked on Splash Mountain, zoom down the tracks of Big Thunder Mountain Railroad, or other attractions with a height requirement with mom while dad hangs with the baby and toddler. Then switcheroo parents. Now dad and the big kids experience a thrill while mom does stroller duty.
As fellow mom of four, I'd be glad to help you with any additional questions you have about your visit to the mouse. Please contact me if you have more.