You can't stop the vomiting if it has started "You can only attempt to STOP if the child is feeling like or retching as if he's about to vomit. Some blow on the child or sprinkle water. It may stem the retching from going to complete process of vomiting temporarily but most will still vomit anyway as long as the cause of the vomiting is not attended to. please take your child back to the hospital preferably a teaching hospital this time, Persistent vomiting in a child whom you have been given drugs to stop vomiting is an Emergency