hi, Sudden bout of vomiting is most commonly caused by a tummy infection, such as gastroenteritis. This is usually brought on by a virus, which may also give your child diarrhoea.Congestion or a respiratory infection, such as a cold, can lead to vomiting It might be exaggreted while you were travelling. Motion sickness happens when there s a disconnect between what your toddler sees and what she/he senses with the motion-sensitive parts of her body, such as her inner ears and some nerves. i will tell you what to do next time when you face this same issue- A.Avoid solid foods for the first 24 hours or so of vomiting. B.Prevent dehydration by making sure your toddler gets enough fluids to make up for what he loses through vomiting. C.Schedule plenty of stops during your trips to give your toddler a chance to get some fresh air and calm his/her tummy. D.Give him/her a small snack before the trip – having something in her stomach will help. E.Offer plenty of fluids to keep her hydrated; otherwise she may get headache or even dizzy or weak, which will only make her more miserable. If condition is serious please consult a doctor ASAP. hope it was helpful. thanks