Viruses cause most illnesses that result in vomiting or diarrhea. Bacteria, parasites, dietary changes or medications may also be responsible. Unlike older children and adults, who usually recover from these illnesses in 24 to 48 hours, infants and toddlers can take several days.

The worst part of the vomiting is usually over in a matter of hours; messy stools may last several days. But the main concern during the worst of the illness is preventing the infant from becoming dehydrated. Signs of dehydration include decreased urine, dry mouth, sunken eyes and lethargy.

A young infant can become dehydrated in as little as four hours if the symptoms are severe. Keep track of urine output. If your baby isn't taking fluids well and has gone several hours without detectable urine output (most babies have six to eight wet diapers a day), contact your healthcare provider for information and advice.