Whether or not your child's diarrhea warrants a visit to the doctor depends on a number of factors:

Dehydration: The most important thing to consider is whether the child is at risk of being dehydrated, says Dr. Neuspiel. Keep an eye on how much fluid the child is taking in and watch out for these signs of dehydration: the child is not urinating as much as normal or has fewer wet diapers; the child cries but no tears come out; the inside of the child's mouth is dry or pasty; the child's eyes are sunken or the skin is doughy. “These are all dangerous signals for dehydration and would need immediate attention. If you suspect your child is dehydrated, see your doctor immediately.” Children who are significantly dehydrated and not able to drink enough may need to get an intravenous catheter put in to get fluids for several hours until they are able to safely go home. Occasionally they will require hospitalization.

High fever and/or vomiting: If a child starts running a high fever, that's cause to see a doctor, since it may be due to a bacterial infection and require antibiotic treatment. If a child has diarrhea with vomiting and can't keep down any liquid, that may also be cause for concern and would require a doctor's visit.

Bloody diarrhea: A streak of blood, which is caused by rectal irritation, is no cause for alarm, says Dr. Neuspiel. However, if blood is mixed in with the diarrhea, then it may be more cause for concern. “Call your doctor if the child has blood or mucus in the stools or severe abdominal or stomach pain, which could be due to bacterial causes,” says Dr. Gigante.