Suckling infants throw up because they swallow a lot of air along with the milk. So, rather than vomiting, they are really just doing very wet burps. But slightly older children do seem to be more prone to vomiting than adults, and it’s likely this has evolved as a protective strategy. For adults, the calorie value of slightly gone-off food or weird berries may have outweighed the risk from the toxins. But children are more vulnerable to food poisoning and disease because of their lower body weight and less developed immune systems. Throwing up at the first sign of trouble represents a bettersafe-than-sorry approach.