Most times a child will have a stomach ache and be complaining of stomach pain which is usually nothing serious and resolves on it's own within a week or two.
If the child just has a tummy ache or stomach ache or the stomach flu then all you can really do is make sure the child gets plenty of rest, keeps hydrated and keep them on a bland diet.
If it's just the stomach flu or stomach ache then it should resolve in a week or two and if it's just a tummy ache as a result of eating too much candy then it should resolve within a day or two.
However if your child is complaining of even more severe pain in their stomach then you might want to take the child to his/her pediatrician or the emergency room or urgent care to get checked out.
If your child is complaining of persistent pain on the right side of the abdomen then it could be appendicitis which needs immediate medical attention.
Or if the child is complaining of stomach pain in one spot of the stomach then it should be checked out.