You can read an extensive answer to a very similar question
HERE.
In addition to the many rides that will accommodate three or more people in a single vehicle, there are several that, while the cars are most comfortable for two, three can squeeze in together. For example, in the Haunted Mansion, Peter Pan, Winnie the Pooh, Spaceship Earth, Journey into the Imagination, and others, an average adult could fit in the ride vehicle with two medium-sized kids. Or, as I suggested in the previous post, you could have the kids ride in one car together with you right behind them.
The main attraction that would likely be untenable for you is the Tomorrowland Indy Speedway. This ride really only fits two people and one of the people must be at least 52" tall (unlikely for an 8-year-old). Other than needing to skip the Speedway, there would be some way for you to experience just about every other attraction.
Have a great trip!