If a member of your group cannot (or chooses not to) ride an attraction—and is unable to wait alone for the rest of your group—you can request a “Rider Switch” from a cast member at the entrance to the attraction. With a Rider Switch, an adult can supervise a non-rider while the rest of the group waits in the queue and experiences the attraction. When that riding-group reunites with the non-riders, the adult who has not yet experienced the attraction may use the Rider Switch to return with a riding-companion and bypass the standby queue to the attraction.
For more on Rider Switch or traveling with young children in general check-out our 5 Tips for Visiting Disneyland Resort with Young Children.