What Causes Blood In Stool?

Dear Doctor, my son named Sameer of 03 years of age and normally growing. but for few months in his stool fresh blood is some time noticed. i have now got his stool detailed report.according to the said report every thing is ok. but i dont understand that why fresh blood is there.kindly guide me that what are the causes of this.we have never notice constipation problem with him. he drinks dry milk named niddo along the bread etc.