It is looking like Gastritis
as the child is having vomitings, fever and foul smelling gas. For vomitings you can give antiemetic in prescribed dosage and for fever you give the advised tylenol and you do tepid sponging with lukewarm water as there is high grade fever and you can give sips of oral rehydrating fluids in equal amounts of losses in vomitings to prevent dehydration
and consult your Pediatrician
for further specific treatment.