I too am a mother of four children, and we have a similar range of ages! One of the many reasons we love vacationing at Walt Disney World Resort is that there really is something for the entire family to do. We recently returned from a trip with our older children and our 2 year old so I do have some suggestions for you.
First, we make good use of
Disney’s Rider Switch Service. This allows one adult to accompany the older children on the attraction, while the second adult waits with the younger child. After the first half of the family is done with their ride, we “switch” the adult. The second adult can then take two of the three older children on the attraction again. This allows both my husband and I to enjoy all the attractions and the older kids get a second ride!
We have found that for most attractions where the 2 year old is unable to ride, there is another attraction nearby suitable for the little one. When my boys ride Space Mountain, the baby and I take a spin on the Tomorrowland Transit Authority PeopleMover. If they are visiting the Seven Dwarfs Mine Train, the baby gets a ride on Prince Charming Regal Carrousel, at Splash Mountain we let her play in The Laughing Place play area under the Frontierland Train Station. If there is not a conveniently located attraction, we will often take the baby for a stroll through nearby shops or maybe use that time for a diaper change or snack.
After everyone has had their fun, we visit something we can all do together. Some of my daughter's favorites from our vacation included: The Barnstormer at Magic Kingdom, Kilimanjaro Safaris at Disney's Animal Kingdom, The Seas with Nemo & Friends at Epcot, and Disney Junior - Live on Stage! at Disney's Hollywood Studios. We have used these techniques as each of our children has gotten older and I truly feel like everyone has a magical vacation!