Thank you for your query on Healthcare Magic.
This presentation is looking like a variant of motion sickness
Just before half an hour of journey, you can give an oral medication consisting of promethazine
in prescribed dosage to prevent the occurrence of motion sickness.
If the child continues to have vomitings even after the completion of journey you can repeat the promethazine every 8th hourly in prescribed dosage.
Therefore I suggest you to consult your Pediatrician
for the prescription of medication.
Hope I have answered your query.