You are probably thinking correctly that abdominal distention in your child is consequence of stomach virus. Abdominal distention in infants can be result from normal causes and from various health conditions and in your case that is stomach virus. One more cause of abdominal distention that occurs frequently in infants and does not indicate a health problem is swallowing excess air. This is most likely to occur during feeding or crying and could result in a distended abdomen.
Colic might also result in abdominal distention and my sister’s baby had colic few months ago so I am familiar with this condition.
Since it has been a while from the time you have posted this you could share with us what has happened in the end and what was the cause of abdominal distention in your three year old.