Your child vomitings are due to acute gastritis
You can give antiemetic like ondansetron or domperidone
in prescribed dosage to stop vomitings immediately.
Give sips of oral rehydrating solutions like Pedialyte to prevent dehydration
Monitor his hydration status by urine output, skin turgor and activity.
Consult your Pediatrician
for the assessment and specific management.
Hope I have answered your query.