UpToDate states that bloody stools in toddlers are a symptom of an anal fissure or intolerance to soy protein or milk. Bloody stools often come from the stomach and small intestine or the rectum, colon and anus. Even though bloody stools aren't always a serious condition, the toddler should still see a pediatrician.
Anal fissures are cracks or fissures in the anus that can occur whenever the toddler passes a hard or large stool, notes UpToDate. Indications that a toddler might have an anal fissure include pain or grunting during a bowel movement and the appearance of bright red blood with wiping or on the stool itself.
According to UpToDate, milk allergies are caused by a sensitivity to the protein in soy or cow's milk. The allergy most often develops after the toddler starts on a formula. Milk allergies have also been known to develop in infants who are breastfed by a mother who consumes soy protein or cow's milk. Soy protein and milk intolerance usually clears up by the time the child turns one. Indications that a child might have a milk allergy include diarrhea, vomiting and bloody stools.
Additional and less common causes of blood in a toddler's stool include infectious diarrhea, inflammatory bowel disease, a bowel obstruction and juvenile polyps.