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You have only mentioned about the undigested food particles only. To come to a conclusion , the complete report has to be reviewed.
Anyways some amount of undigested food particles are found in stool analysis , which is normal. If it is high, it suggests the food transit in gut is rapid. This usually is seen in malabsorption
secondary digestive enzyme deficiency
( pancreatic or small intestinal enzymes).
Presence of fat in stools favors the diagnosis of Malabsorption ( Fat is invariably present in the stool in all forms of malabsorption.
As you have mentioned only the undigested material came to your attention, i would assume that rest of the report is normal. In that case, there shall be no major problem with your child and the undigested material in stool is an occasional and a normal finding.
Dont worry, your child is gonna be fine.
Wish your son a speedy recovery