There are many things you can do to your workshops for them to have success there too. For instance, visuals are very helpful for all kids but especially for kids with special needs. If you have an art project break it down step by step with the class watching, cooking or science projects having directions/recipe enlarged and pictures added. I know that these may take more time but you will doing a lot of prep for the other class
I have used additional teachers to be sort of one on ones in Sunday school and that has worked well. I know that means more volunteers but if you are putting them all together you are needing more volunteers too.
Also if children have severe disablities they are usually are eligible for personal care attendants(PCA's). PCA's will not only take the children when parents are gone but also in church for Sunday school. PCA's will adapt the curric. as they go. If they are not severe then I see rotation working well with them, especially the younger ages as the differences between preschool to about first grade are not as large/obvious. It certainly depends on the disablity too!