I would not suggest Simpsons if your child feels motion sick on rides. I did not get the 'push back into your seat negative or positive G feelings' from a roller coaster.
I have seasonal vertigo (related to allergies!) and I find I got that 'dizzy' ugh feeling during Simpsons (this was in CA so I do not know if the ride is different in FL). Because this is something I can experience even standing still, I have a few suggestions that have worked for me to lessen the impact on the rest of your day.
If you do not get car sick, can handle being a passenger in a van without windows or ride in a bus comfortably, close your eyes! This might not be the best choice for you. This can cause other symptoms of motion sickness, similar to 'reading in a car' or riding backwards on a train.
Try not to move your head to the left or right, especially in rides that can simulate weightlessness. (like Mission: Space in Epcot)
Another suggestion would be to stare at a stationary thing (not the screen!)
I do a combination of all three. I will sit very still, close my eyes, then if I feel 'car sick' I open them and stare at something stationary, then close my eyes again, repeat.
I'm not going to ride Simpsons when I got to US next month.