Thanku for your query.
Well motion sickness
is associated with nausea vomiting
and vague abdominal discomfort that kids generally interpret as abdominal pain
followed by malaise
and headache .Excessive stimulation of vestibular system
by motion is the primary cause.Few factors may increase the risk of developing motion sickness
Emotional factors like fear,anxiety
For this u have to inform the bus driver to keep vehicle well ventilated and ask your son to sit in front and avoid bright sunlight exposed places in bus also to take small quantity of liquids and food at regular interval, avoid large meals .
I hope I have answered your query