I have a 3 year old, started vomiting almost 24 hr ago, no fever, keeping hydrated. is it just a 24 hr bug he's experiencing? if, when should i worry?

Could be.: Viruses are common causes for vomiting, poor digestion and loose stools. Fever is not always present. Food items and "other" ingestions may contribute. If your 3 year old is otherwise doing well keeping things down, you should be in the clear for a quick recovery. Don't be surprised if appetite is not up to speed. Concern: if vomiting returns repeatedly & after stomach rest, not tolerating fluids.