Intermittent, ongoing vomiting usually does not increase a child's risk of dehydration or other problems as long as the child is able to hold down food and fluids between vomiting. Some young children vomit every once in a while for no apparent reason, and this does not cause any long-term problems. However, if the vomiting continues, a medical evaluation is recommended to determine whether there is an underlying cause. The more time that passes between episodes of vomiting, the less concerning it is.
WebMD Medical Reference from Healthwise