Is a chronic stomach ach in children be a sign of diabetes?

No. Lots of causes of chronic abdominal pain in kids. If a parent has migraine child can have abdominal migraine. Pediatrician or family doctor can sort this out for you.
Oh the achin' belly. Most tummy aches in kids are not serious. We do investigate all complaints of abdominal discomfort. Diabetes does not usually present with pain in the stomach area. Remember good diet and appropriate potty time helps most tummy aches.