Vomiting with no fever in a sleeping 2 year old. maybe something he ate?

Likely viral: Usually these things are viral and are short-lived and self-limited, meaning they go away spontaneously. They are highly contagious so strict hand-washing is in order. Dehydration is the main threat so push fluids even if he/she doesn't want to eat. Big concerns are fever over 100.6; or complaints of pain. Intermittent cramps are expected but if there is progressing unrelenting pain seek help.