The receptors in your inner ear feed you information about how fast and which directions your head is moving.
When you or your child gets motion sickness it is because your head movement and your eyes are not organizing well. You might notice that a person who gets motion sickness easily requests to drive or sit in the front of the car. This allows the brain to get more visual information. The person will be able to coordinate the visual information with movement input and decease sickness.
Vestibular sensory input is often associated with a person's sense of balance. But the vestibular system is essential to support:
Resources:
https://www.griffinot.com/vestibular-system/
Living Sensationally by Dr. Winnie Dunn