Yes, diarrhea can occur after a stomach bug in a 4-year-old child. It is normal for there to be some discomfort following a bout of gastroenteritis. As long as your child is eating and drinking (even if less than usual) and you notice a gradual improvement every day, there is no need to worry. It's recommended to continue giving Tylenol as directed by your pharmacist based on your child's weight. Stick to light foods like soups, broths, crackers, toast with a little butter, and avoid heavy or sugary foods like red meat and undiluted fruit juices. You should see improvement each day.