We've seen a nasty stomach bug going around lately. No fun. If you're child comes down with it try to start clear fluids as early as possible. If they are having a hard time keeping anything down go slow, giving them as little as a teaspoon every 15 minutes or so. Anything is better than nothing. A child should have at least 3 wet diapers a day or one wet diaper every 10 hours. Fewer would indicate dehydration and likely need IV fluids.
For more information on gastroenteritis (the fancy word for the stomach flu) go here.
If you really want to know more, go here.