Hi Stephen,
Thank you so much for visiting the Disney Parks Moms Panel with your question! We on the panel love helping guests to plan magical vacations.
I am happy to tell you that yes, the kind of service you are asking about exists at Walt Disney World. It is called
Rider Switch Service. Do visit the link that I just provided for details. In essence, you will ask the first cast member you see at an attraction about Rider Switch Service for the attraction. Generally, one adult and the child or children who are too small will wait outside the attraction while the other adult and any others who can ride go through the queue and experience the attraction. When the first group is done, they locate the group who is waiting and hand off a Rider Switch pass. The adult who waited initially will be able to experience the attraction without going through the regular queue, and can bring one other person along.
The Rider Switch Service link above gives a list of attractions that offer this service. You might also want to check out this
Disney Parks Blog post for a list of attractions with height limits to see which attractions might be restricted for your children.
I hope that this information is helpful for you, Stephen! Have a great time planning, and please do let us know if you have any further questions.