A 3 year old child has had vomiting and loose stools for 24 hours. She is complaining of intermittent abdominal pain but there is no blood in her vomit or stools. She has been sipping juice regularly at home but is off food.
On examination she is alert, and her observations and urine dip are normal. Her abdomen is soft with no masses or tenderness.
What is the most likely diagnosis?