Gee, I think it all depends on what you describe as a stomach ache. I get mild to moderate crampy/gassy feelings off and on all the time, but I would not call them "stomach aches" because I know that they are just my gut churning. Usually it is not an issue, but sometimes it is more pronounced to me. People with IBS are extremely sensitive to what is going on in their gut, so they perceive quite a bit of normal activity as a stomach ache.
Plus, when you are dealing with kids, it is hard to tell if they are having serious pain, or if they are just very focused on their gut activity. This can be especially true when they have had a history of serious gut problems. It can give them a reason to be on a high alert.
As both a parent and a patient, I know it can be difficult to sort out the usual stuff from something to pay attention to. With kids we don't want them to feel like they are so fragile that they need to see the doctor for every little twinge. But, we also want to be sure that they alert us to serious symptoms.
Bottom line, if he experiences pain that is significant, frequent or constant, or with other symptoms, then you should bring it to the attention of the doctor. Fleeting discomfort or mild indigestion type feelings can be placed in the "wait and see" type of thing. Especially after having major abdominal surgery, this stuff is common.
Don't you wish you had x-ray vision!?!
Jan