Anal Fissure: This is a common cause of rectal bleeding in infants, often due to constipation or hard stools causing a tear in the anal mucosa. The age of the child and the nature of the bleeding (usually a small amount of bright red blood) support this diagnosis.

Allergic Colitis: This condition, often associated with cow's milk protein allergy, can cause blood in stool due to inflammation of the colon. It's a common cause of rectal bleeding in infants.
Gastroenteritis: Viral or bacterial infections can lead to inflammation of the gastrointestinal tract, resulting in bloody stools. The presence of other symptoms like diarrhea, vomiting, and fever would support this diagnosis.
Intussusception: Although more common in older infants, intussusception (where a part of the intestine slides into another) can cause bloody stools and is a significant consideration due to its potential for serious complications.

Intestinal Intussusception: As mentioned, this condition requires urgent diagnosis and treatment to prevent complications like bowel ischemia and necrosis.
Meckel's Diverticulum: A congenital anomaly of the small intestine that can cause significant bleeding due to the presence of ectopic gastric mucosa. Although rare, it's a critical diagnosis not to miss due to the potential for severe blood loss.
Hirschsprung's Disease: A congenital condition characterized by the absence of ganglion cells in the distal bowel, leading to obstruction and potentially enterocolitis, which can cause bloody stools.

Juvenile Polyps: Although rare in infants, these benign growths in the colon can cause intermittent bleeding.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis are rare in infants but can present with bloody stools among other symptoms.
Vascular Malformations: Rare congenital conditions that can cause bleeding in the gastrointestinal tract.